Pack of 50 Summary/Response Forms for the GARS-3. The Gilliam Autism Rating Scale (GARS-3), now in its third edition, is one of the most widely used instruments for the assessment of Autism Spectrum Disorder in the world. The GARS-3 assists teachers, parents, and clinicians in identifying autism in individuals and estimating its severity. Items on the GARS-3 reflect the 2013 diagnostic criteria for Autism Spectrum Disorder adopted by the APA and published in the Diagnostic and Statistical Manual of Mental Disorders–Fifth Edition (DSM-5). The GARS-3 yields standard scores, percentile ranks, severity level, and probability of Autism.