The goals of this diagnostic study are to determine how accurate general pediatricians are in autism spectrum disorder (ASD) diagnostic assessment and which children might be best suited for this type of assessment. The investigators will also evaluate the use of a new virtual diagnostic tool, the Autism Assessment for Preschoolers with Language Element Sequence (AAPLES).

The investigators will recruit twenty general pediatricians from across Ontario, Canada, as well as 200 of their patients (maximum 10 per pediatrician) who have been referred with possible ASD. The general pediatrician will complete their assessment and decide on a diagnosis, but will not tell the family. The ASD expert team, consisting of a developmental paediatrician and a psychologist, will also perform a diagnostic assessment without knowing the general pediatrician's opinion. The team will inform the family of their diagnostic opinion. Investigators will determine the diagnostic agreement between the two assessments. They will then determine which of the child's characteristics (age, sex, racial/ethnic background, ASD features, developmental delays, having a sibling with ASD) predict agreement in diagnosis.

Some children in the study will have the option of undergoing an additional virtual autism diagnostic assessment using the AAPLES. The clinician administering the AAPLES will not know the results of the other assessments. The investigators will measure diagnostic agreement between the clinician administering the AAPLES and the expert team.

Increasing rates of autism spectrum disorder (ASD) diagnosis have contributed to lengthy waits for expert diagnostic assessment that negatively impact ASD outcomes. Many ASD diagnostic guidelines state that an expert team is needed to make the diagnosis; although some children currently receive their diagnosis from a community-based clinician, e.g. a general paediatrician. There are very few studies of the accuracy of general pediatricians in diagnosing ASD.

The aims of this project are to:

1. determine accuracy of general pediatrician ASD diagnosis compared to an expert team assessment;
2. to determine child features associated with accurate diagnosis by general pediatricians (possible features include: child's age; gender; cultural background; ASD features; developmental delays; and having a sibling with ASD; pediatrician certainty; virtual versus in person assessment);
3. to identify general pediatrician factors associated with accurate diagnosis (possible features include pediatrician years in practice, gender, rurality, extra training in child development, use of tools in the assessment, time spent on the assessment);
4. to determine the concordance between an assessment with the AAPLES virtual tool and the expert team assessment.

Investigators will recruit twenty general pediatricians from across Ontario, as well as 200 of their patients (10 per general pediatrician) who have been referred with possible ASD. The general pediatrician will complete their assessment and decide on a diagnosis, but will not tell the family. The ASD expert team, consisting of a developmental paediatrician and a psychologist, will also perform a diagnostic assessment without knowing the general pediatrician's opinion. The team will inform the family of their diagnostic opinion. Investigators will determine the diagnostic agreement between the two assessments. They will then determine which of the child's characteristics (age, sex, cultural background, ASD severity, developmental delays, having a sibling with ASD) predict agreement in diagnosis. Exploratory analyses will be done on pediatrician factors associated with diagnostic accuracy, analyzing pediatrician years in practice, gender, rurality, extra training in child development, use of tools in the assessment, and time spent on the assessment. Children meeting the criteria for the AAPLES will be offered an additional virtual assessment where a trained clinician, blinded to the previous assessment results, will administer the AAPLES and record their diagnostic opinion. Investigators will measure agreement between this opinion and the expert team.

Child Inclusion Criteria:

• Must be referred to a general pediatrician participating in the study with any of the following issues: 1) Failed 18-month developmental screen (other than isolated motor delay); 2) Speech/language delay; 3) Social/emotional delay/concern; 4) Behavioral concerns, inattention, hyperactivity, or impulsivity; 5) Global developmental delay/concern; 6) A referral with a query of ASD.
• Age <5 years 6 months
• Resident of Ontario, Canada (support for travel is available for participants who live >100 km from Toronto)

Exclusion Criteria:

• Child has already received a diagnosis of ASD

For the AAPLES exploratory objective:

Inclusion Criteria:

• Child has a developmental age of 36 months or more (determined on Mullen Scales of Early Learning)
• Child has flexible phrase speech

Exclusion Criteria:

- Child has previously completed a virtual ASD diagnostic assessment

General pediatricians are eligible for participation if they: 1) practice in Ontario; 2) see at least one child per month with possible ASD; and 3) have not completed subspecialty training in developmental pediatrics. Consecutive children with possible ASD meeting inclusion criteria will be enrolled from each participating pediatrician (maximum of 10 per pediatrician).