Although many alternative therapies and interventions are available, few are supported by scientific studies. Treatment approaches have little empirical support in quality-of-life contexts, and many programs focus on success measures that lack predictive validity and real-world relevance. Scientific evidence appears to matter less to service providers than program marketing, training availability, and parent requests. Some alternative treatments may place the child at risk. A 2008 study found that compared to their peers, autistic boys have significantly thinner bones if on casein-free diets; in 2005, botched chelation therapy killed a five-year-old child with autism. There has been early research looking at hyperbaric treatments in children with autism.

Although popularly used as an alternative treatment for people with autism, there is no good evidence that a gluten-free diet is of benefit. In the subset of people who have gluten sensitivity there is limited evidence that suggests that a gluten free diet may improve some autistic behaviors.

Educational interventions can be effective to varying degrees in most children: intensive ABA treatment has demonstrated effectiveness in enhancing global functioning in preschool children and is well-established for improving intellectual performance of young children. Similarly, teacher-implemented intervention that utilizes an ABA combined with a developmental social pragmatic approach has been found to be a well-established treatment in improving social-communication skills in young children, although there is less evidence in its treatment of global symptoms. Neuropsychological reports are often poorly communicated to educators, resulting in a gap between what a report recommends and what education is provided. It is not known whether treatment programs for children lead to significant improvements after the children grow up, and the limited research on the effectiveness of adult residential programs shows mixed results. The appropriateness of including children with varying severity of autism spectrum disorders in the general education population is a subject of current debate among educators and researchers.

No medications directly treat the core symptoms of AS. Although research into the efficacy of pharmaceutical intervention for AS is limited, it is essential to diagnose and treat comorbid conditions. Deficits in self-identifying emotions or in observing effects of one's behavior on others can make it difficult for individuals with AS to see why medication may be appropriate. Medication can be effective in combination with behavioral interventions and environmental accommodations in treating comorbid symptoms such as anxiety disorder, major depressive disorder, inattention and aggression. The atypical antipsychotic medications risperidone and olanzapine have been shown to reduce the associated symptoms of AS; risperidone can reduce repetitive and self-injurious behaviors, aggressive outbursts and impulsivity, and improve stereotypical patterns of behavior and social relatedness. The selective serotonin reuptake inhibitors (SSRIs) fluoxetine, fluvoxamine, and sertraline have been effective in treating restricted and repetitive interests and behaviors.

Care must be taken with medications, as side effects may be more common and harder to evaluate in individuals with AS, and tests of drugs' effectiveness against comorbid conditions routinely exclude individuals from the autism spectrum. Abnormalities in metabolism, cardiac conduction times, and an increased risk of type 2 diabetes have been raised as concerns with these medications, along with serious long-term neurological side effects. SSRIs can lead to manifestations of behavioral activation such as increased impulsivity, aggression, and sleep disturbance. Weight gain and fatigue are commonly reported side effects of risperidone, which may also lead to increased risk for extrapyramidal symptoms such as restlessness and dystonia and increased serum prolactin levels. Sedation and weight gain are more common with olanzapine, which has also been linked with diabetes. Sedative side-effects in school-age children have ramifications for classroom learning. Individuals with AS may be unable to identify and communicate their internal moods and emotions or to tolerate side effects that for most people would not be problematic.

There is no known cure for autism, although those with Asperger syndrome and those who have autism and require little-to-no support are more likely to experience a lessening of symptoms over time. The main goals of treatment are to lessen associated deficits and family distress, and to increase quality of life and functional independence. In general, higher IQs are correlated with greater responsiveness to treatment and improved treatment outcomes. Although evidence-based interventions for autistic children vary in their methods, many adopt a psychoeducational approach to enhancing cognitive, communication, and social skills while minimizing problem behaviors. It has been argued that no single treatment is best and treatment is typically tailored to the child's needs.

Intensive, sustained special education programs and behavior therapy early in life can help children acquire self-care, social, and job skills. Available approaches include applied behavior analysis, developmental models, structured teaching, speech and language therapy, social skills therapy, and occupational therapy. Among these approaches, interventions either treat autistic features comprehensively, or focus treatment on a specific area of deficit. Generally, when educating those with autism, specific tactics may be used to effectively relay information to these individuals. Using as much social interaction as possible is key in targeting the inhibition autistic individuals experience concerning person-to-person contact. Additionally, research has shown that employing semantic groupings, which involves assigning words to typical conceptual categories, can be benevficial in fostering learning.

There has been increasing attention to the development of evidence-based interventions for young children with ASD. Two theoretical frameworks outlined for early childhood intervention include applied behavioral analysis (ABA) and the developmental social-pragmatic model (DSP). Although ABA therapy has a strong evidence base, particularly in regard to early intensive home-based therapy. ABA's effectiveness may be limited by diagnostic severity and IQ of the person affected by ASD. The Journal of Clinical Child and Adolescent Psychology has deemed two early childhood interventions as “well-established”: individual comprehensive ABA, and focused teacher-implemented ABA combined with DSP.

Another evidence-based intervention that has demonstrated efficacy is a parent training model, which teaches parents how to implement various ABA and DSP techniques themselves. Various DSP programs have been developed to explicitly deliver intervention systems through at-home parent implementation.

A multitude of unresearched alternative therapies have also been implemented. Many have resulted in harm to autistic people and should not be employed unless proven to be safe.

In October 2015, the American Academy of Pediatrics (AAP) proposed new evidence-based recommendations for early interventions in ASD for children under 3. These recommendations emphasize early involvement with both developmental and behavioral methods, support by and for parents and caregivers, and a focus on both the core and associated symptoms of ASD.

The ideal treatment for AS coordinates therapies that address core symptoms of the disorder, including poor communication skills and obsessive or repetitive routines. While most professionals agree that the earlier the intervention, the better, there is no single best treatment package. AS treatment resembles that of other high-functioning ASDs, except that it takes into account the linguistic capabilities, verbal strengths, and nonverbal vulnerabilities of individuals with AS. A typical program generally includes:

- A positive behavior support procedure includes training and support of parents and school faculty in behavior management strategies to use in the home and school;

- An applied behavior analysis (ABA) technique called social skills training for more effective interpersonal interactions;

- Cognitive behavioral therapy to improve stress management relating to anxiety or explosive emotions and to cut back on obsessive interests and repetitive routines;

- Medication, for coexisting conditions such as major depressive disorder and anxiety disorder;

- Occupational or physical therapy to assist with poor sensory processing and motor coordination;

- Social communication intervention, which is specialized speech therapy to help with the pragmatics of the give and take of normal conversation.

Of the many studies on behavior-based early intervention programs, most are case reports of up to five participants and typically examine a few problem behaviors such as self-injury, aggression, noncompliance, stereotypies, or spontaneous language; unintended side effects are largely ignored. Despite the popularity of social skills training, its effectiveness is not firmly established. A randomized controlled study of a model for training parents in problem behaviors in their children with AS showed that parents attending a one-day workshop or six individual lessons reported fewer behavioral problems, while parents receiving the individual lessons reported less intense behavioral problems in their AS children. Vocational training is important to teach job interview etiquette and workplace behavior to older children and adults with AS, and organization software and personal data assistants can improve the work and life management of people with AS.

Medications are used to address certain behavioral problems; therapy for children with PDD should be specialized according to the child's specific needs.

Some children with PDD benefit from specialized classrooms in which the class size is small and instruction is given on a one-to-one basis. Others function well in standard special education classes or regular classes with support. Early intervention, including appropriate and specialized educational programs and support services, play a critical role in improving the outcome of individuals with PDD.

Several prenatal and perinatal complications have been reported as possible risk factors for autism. These risk factors include maternal gestational diabetes, maternal and paternal age over 30, bleeding after first trimester, use of prescription medication (e.g. valproate) during pregnancy, and meconium in the amniotic fluid. While research is not conclusive on the relation of these factors to autism, each of these factors has been identified more frequently in autistic children compared to their non-autistic siblings and other normally developing youth.

Low vitamin D levels in early development has been hypothesized as a risk factor for autism.

There is no known "cure" for PDD-NOS, but there are interventions that can have a positive influence. Early and intensive implementation of evidence-based practices and interventions are generally believed to improve outcomes. Most of these are individualized special education strategies rather than medical or pharmaceutical treatment; the best outcomes are achieved when a team approach among supporting individuals is utilized.

Some of the more common therapies and services include:

- Visual and environmental supports, visual schedules

- Applied behavior analysis

- Discrete trial instruction (part of applied behavior analysis)

- Social stories and comic strip conversations

- Physical and occupational therapy

Treatments for HFA address individual symptoms, rather than the condition as a whole. For instance, to treat anxiety, which is often associated with HFA, the main treatment is cognitive behavior therapy. While this is the tested and approved treatment for anxiety, it does not quite meet the needs associated with the symptoms of HFA. There is very little discussion of the parent's role in anxiety intervention for children and teenagers. A revised version of cognitive behavior therapy has parents and teachers acting in a role as social coaches to help the children or young adults cope with the issues they are facing. There have been several trials proving that the involvement of parents in the lives of the children affected with anxiety associated with HFA is important.

No single intervention exists to aid individuals with high-functioning autism. However, there are proactive strategies, such as self care and self-management, designed to maintain or change behavior to make living with high functioning autism easier. Self-management strategies aim to provide skills necessary to self-regulate behavior, leading to greater levels of independence. Improving self-management skills allows the individual to be more self-reliant rather than having to rely on an external source for supervision or control. Self-monitoring is a framework, not a rigid structure, designed to encourage independence and self-control. Self-monitoring is not for everyone. It requires the attention and dedication of the individual with high-functioning autism as well as the individual overseeing the progress.

A framework for self-monitoring is provided below

- Identify positive target behaviors

- Establish an alternative behavior that is positive/constructive

- Establish a self-recording sheet

- Individuals can make sure to stay on track with intended goals

- Set goals and keep them

The goal of self-monitoring is to enforce self-monitoring independently without prompting.

Regression in autism spectrum disorders is well documented; attribution of regression to environmental stress factors may result in a delay in diagnosis. The apparent onset of regressive autism is surprising and distressing to parents, who often initially suspect severe hearing loss. A controversy occurred following a fraudulent study linking MMR vaccine to autism, but since then, studies have shown no connection between autism and the MMR vaccine. There are also studies being done to test if certain types of regressive autism have an autoimmune basis.

Regressive autism occurs when a child appears to develop typically but then starts to lose speech and social skills, typically between the ages of 15 and 30 months, and is subsequently diagnosed with autism. Other terms used to describe regression in children with autism are autism with regression, autistic regression, setback-type autism, and acquired autistic syndrome. There is no standard definition for regression, and the prevalence of regression varies depending on the definition used. Some children show a mixture of features, with some early delays and some later losses; and there is evidence of a continuous spectrum of behaviors, rather than a black-and-white distinction, between autism with and without regression. According to the definitions in the DSM-5 the term "regressive autism" can refer to any type of autism spectrum disorder that involves regression, including Childhood Disintegrative Disorder.

Loss of language and skills related to social interaction and self-care are serious. The affected children face ongoing disabilities in certain areas and require long term care. Treatment of CDD involves both behavior therapy, environmental therapy and medications.

- Behavior therapy: The main aim of Applied Behavior Analysis (ABA) is to systematically teach the child to relearn language, self-care and social skills. The treatment programs designed in this respect "use a system of rewards to reinforce desirable behaviors and discourage problem behavior." ABA programs may be designed by a board-certified specialist in behavior analysis called a "BCBA" (Board Certified Behavior Analyst), but ABA is also widely used by a number of other health care personnel from different fields like psychologists, speech therapists, physical therapists and occupational therapists with differing levels of expertise. Parents, teachers and caregivers are instructed to use these behavior therapy methods at all times.

- Environmental Therapy: Sensory Enrichment Therapy uses enrichment of the sensory experience to improve symptoms in autism, many of which are common to CDD.

- Medications: There are no medications available to directly treat CDD. Antipsychotic medications are used to treat severe behavior problems like aggressive stance and repetitive behavior patterns. Anticonvulsant medications are used to control seizures.

The diagnostic category pervasive developmental disorders (PDD), as opposed to specific developmental disorders (SDD), refers to a group of five disorders characterized by delays in the development of multiple basic functions including socialization and communication. The pervasive developmental disorders are: All autism spectrum disorders and Rett syndrome.

The first four of these disorders are commonly called the autism spectrum disorders; the last disorder is much rarer, and is sometimes placed in the autism spectrum and sometimes not.

The onset of pervasive developmental disorders occurs during infancy, but the condition is usually not identified until the child is around three years old. Parents may begin to question the health of their child when developmental milestones are not met, including age appropriate motor movement and speech production.

There is a division among doctors on the use of the term PDD. Many use the term PDD as a short way of saying PDD-NOS (Pervasive developmental disorder not otherwise specified). Others use the general category label of PDD because they are hesitant to diagnose very young children with a specific type of PDD, such as autism. Both approaches contribute to confusion about the term, because the term PDD actually refers to a category of disorders and is not a diagnostic label.

Although little is known about the biological basis of autism, studies have revealed structural abnormalities in specific brain regions. Regions identified in the "social" brain include the amygdala, superior temporal sulcus, fusiform gyrus area and orbitofrontal cortex. Further abnormalities have been observed in the caudate nucleus, believed to be involved in restrictive behaviors, as well as in a significant increase in the amount of cortical grey matter and atypical connectivity between brain regions.

There is a mistaken belief that some vaccinations, such as the MMR, the measles/mumps vaccine, may cause autism. This was based on a research study published by Andrew Wakefield, which has been determined fraudulent and retracted. The results of this study caused some parents to take their children off the vaccines; these diseases can cause intellectual disabilities or death. The claim that some vaccinations cause autism has not been proven through multiple large-scale studies conducted in Japan, the United States, and other countries.

Mind-blindness is a cognitive disorder where an individual is unable to attribute mental states to others. As a result of this kind of social and empathetic cognitive deficit, the individual is incapable in putting himself "into someone else's shoes" and cannot conceptualize, understand or predict knowledge, thoughts and beliefs, emotions, feelings and desires, behaviour, actions and intentions of another person. Such an ability to develop a mental awareness of what is in the other minds is known as the theory of mind (ToM), and the "Mind-blindness" Theory asserts that children who delay in this development often are or will be autistic and Asperger's syndrome (AS) patients. In addition to autism and AS, ToM and mind-blindness research has recently been extended to other disorders such as schizophrenia, dementia, bipolar disorders, antisocial personality disorders as well as normal aging.

There is no cure for ASD and proper treatment depends on the case and what is most struggled with. Autism spectrum disorder is like many other disorders where when diagnosed early, can be better treated. Different types of therapy are helpful such as music therapy and physical therapy. Other treatments include auditory training, discrete trial training, facilitated communication, and sensory integration therapy.

A pervasive developmental disorder not otherwise specified (PDD-NOS) is one of the four autism spectrum disorders (ASD) and also one of the five disorders classified as a pervasive developmental disorder (PDD). According to the DSM-IV, PDD-NOS is a diagnosis that is used for "severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific PDD" or for several other disorders. PDD-NOS is often called atypical autism, because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomatology, or all of these. Even though PDD-NOS is considered milder than typical autism, this is not always true. While some characteristics may be milder, others may be more severe.

Treatment of ADHD often includes a combination of psychological, behavioural, pharmaceutical and educational advice and interventions.

Medications commonly used in the treatment of ADHD are primarily stimulants such as methylphenidate and lisdexamphetamine and non-stimulants such as atomoxetine.

SSRI antidepressants may be unhelpful, and could worsen symptoms of ADHD.

However ADHD is often misdiagnosed as depression, particularly when no hyperactivity is present.

There are no objectively definitive statistics about how many people have savant skills. The estimates range from "exceedingly rare" to one in ten people with autism having savant skills in varying degrees. A 2009 British study of 137 parents of autistic children found that 28% believe their children met the criteria for a savant skill, defined as a skill or power "at a level that would be unusual even for 'normal' people". As many as 50 cases of sudden or acquired savant syndrome have been reported.

Males with savant syndrome outnumber females by roughly 6:1, slightly higher than the sex ratio disparity for autism spectrum disorders of 4.3:1.

No widely accepted cognitive theory explains savants' combination of talent and deficit. It has been suggested that individuals with autism are biased towards detail-focused processing and that this cognitive style predisposes individuals either with or without autism to savant talents. Another hypothesis is that savants hyper-systemize, thereby giving an impression of talent. Hyper-systemizing is an extreme state in the empathizing–systemizing theory that classifies people based on their skills in empathizing with others versus systemizing facts about the external world. Also, the attention to detail of savants is a consequence of enhanced perception or sensory hypersensitivity in these unique individuals. It has also been confirmed that some savants operate by directly accessing low-level, less-processed information that exists in all human brains that is not normally available to conscious awareness.

All of the causes of childhood disintegrative disorder are still unknown. Sometimes CDD surfaces abruptly within days or weeks, while in other cases it develops over a longer period of time. A Mayo Clinic report indicates: "Comprehensive medical and neurological examinations in children diagnosed with childhood disintegrative disorder seldom uncover an underlying medical or neurological cause. Although the occurrence of epilepsy is higher in children with childhood disintegrative disorder, experts don't know whether epilepsy plays a role in causing the disorder."

CDD, especially in cases of later age of onset, has also been associated with certain other conditions, particularly the following:

- Lipid storage diseases: In this condition, a toxic buildup of excess fats (lipids) takes place in the brain and nervous system.

- Subacute sclerosing panencephalitis: Chronic infection of the brain by a form of the measles virus causes subacute sclerosing panencephalitis. This condition leads to brain inflammation and the death of nerve cells.

- Tuberous sclerosis (TSC): TSC is a genetic disorder. In this disorder, tumors may grow in the brain and other vital organs like kidneys, heart, eyes, lungs, and skin. In this condition, noncancerous (benign) tumors, hamartomas, grow in the brain.

- Leukodystrophy: In this condition, the myelin sheath does not develop in a normal way causing white matter in the brain to disintegrate.

Current trends in treating the disorder include medications for symptom-based treatments that aim to minimize the secondary characteristics associated with the disorder. If an individual is diagnosed with FXS, genetic counseling for testing family members at risk for carrying the full mutation or premutation is a critical first-step. Due to a higher prevalence of FXS in boys, the most commonly used medications are stimulants that target hyperactivity, impulsivity, and attentional problems. For co-morbid disorders with FXS, antidepressants such as selective serotonin reuptake inhibitors (SSRIs) are utilized to treat the underlying anxiety, obsessive-compulsive behaviors, and mood disorders. Following antidepressants, antipsychotics such as Risperdal and Seroquel are used to treat high rates of self-injurious, aggressive and aberrant behaviors in this population (Bailey Jr et al., 2012). Anticonvulsants are another set of pharmacological treatments used to control seizures as well as mood swings in 13%–18% of individuals suffering from FXS. Drugs targeting the mGluR5 (metabotropic glutamate receptors) that are linked with synaptic plasticity are especially beneficial for targeted symptoms of FXS. Lithium is also currently being used in clinical trials with humans, showing significant improvements in behavioral functioning, adaptive behavior, and verbal memory. Alongside pharmacological treatments, environmental influences such as home environment and parental abilities as well as behavioral interventions such as speech therapy, sensory integration, etc. all factor in together to promote adaptive functioning for individuals with FXS.

Current pharmacological treatment centers on managing problem behaviors and psychiatric symptoms associated with FXS. However, as there has been very little research done in this specific population, the evidence to support the use of these medications in individuals with FXS is poor.

ADHD, which affects the majority of boys and 30% of girls with FXS, is frequently treated using stimulants. However, the use of stimulants in the fragile X population is associated with a greater frequency of adverse events including increased anxiety, irritability and mood lability. Anxiety, as well as mood and obsessive-compulsive symptoms, may be treated using SSRIs, although these can also aggravate hyperactivity and cause disinhibited behavior. Atypical antipsychotics can be used to stabilise mood and control aggression, especially in those with comorbid ASD. However, monitoring is required for metabolic side effects including weight gain and diabetes, as well as movement disorders related to extrapyramidal side effects such as tardive dyskinesia. Individuals with coexisting seizure disorder may require treatment with anticonvulsants.

"Early onset schizophrenia" (EOS) is not childhood schizophrenia, because this term is used to identify adolescence patients who develop first episode of psychosis before the age of 18. Childhood schizophrenia manifests before the age of 13, so it's correct names are "childhood-onset schizophrenia" (COS) and "very early-onset schizophrenia" (VEOS).

Adolescents (teenagers) are persons between the ages of 13 and 18. Children are defined as persons under the age of 13, so the term "early onset schizophrenia" (EOS) is not not appropriate in the article about childhood schizophrenia.

A 2013 review stated that life expectancy for FXS was 12 years lower than the general population and that the causes of death were similar to those found for the general population.

Late talker is a term used for exceptionally bright people who experience a delay in the development of speech. Commonalities include usually being boys, delayed speech development, highly educated parents, musically gifted families, puzzle-solving abilities, and lagging social development. Many high-achieving late talkers were notoriously strong willed and noncompliant as children. Late talkers can often be misdiagnosed early on as having severe ("low-functioning") autism spectrum disorder (a category known simply as "autism", prior to the DSM-5), and careful professional evaluation is necessary for differential diagnosis, according to Darold Treffert and other experts. One major difference between late talkers and low-functioning autistic children is that for late talkers, communication skills automatically reach a normal level and the child requires no further special treatment with regards to speech. Outlook for late talkers with or without intervention is generally favorable. However, late language emergence can also be an early or secondary sign of high-functioning autism spectrum disorder / Asperger syndrome, or other developmental disorders, such as attention deficit hyperactivity disorder, intellectual disability, learning disability, social communication disorder, or specific language impairment.

Einstein syndrome, a term coined by the economist Thomas Sowell, is also sometimes used to describe late talkers. The term is named after Albert Einstein (often said to have been a late talker, though with questionable evidence), whom Sowell used as the primary example of a late talker in his work. Sowell also included Edward Teller, Srinivasa Ramanujan, the mathematician Julia Robinson, Richard Feynman, and the pianists Clara Schumann and Arthur Rubinstein to be in the late talkers group. As a toddler, the scientist John Clive Ward showed similar behavioral traits to those described by Sowell, according to a brief sketch of his biography.

Sowell claimed late talkers are often inaccurately categorized as having an autism spectrum disorder (ASD), and that a small subset of late talkers are highly intelligent children with common characteristics concentrated in music, memory, math or the sciences. However, as reported by Simon Baron-Cohen, such characteristics are often found in high-functioning autism / Asperger syndrome.