Purpose: Only a few studies examined the longitudinal pattern of parent-teacher reports on autism severity and comorbidities in autism spectrum disorder (ASD) and yielded conflicting results. The study's aims were to compare parents and teachers' perception of autism, attention deficit hyperactivity disorder (ADHD) and anxiety symptoms severity in children with ASD, at the start (T1) and end (T2) of the school year, to assess changes in their perception over time and to examine correlations between their reports. Methods: The study included 73 participants, (M = 61), aged 2:10 - 7:6 years (M = 4:10, SD = 1:0), who attended ASD special education classes and were receiving intensive interventions. Parents and teachers completed measures of autism severity and ADHD and anxiety symptoms at T1 and T2. Results: Teachers, in comparison to parents, rated more severe social-communication impairments and inattention symptoms at T1, but not at T2. A significant improvement in teachers' ratings of autism and inattention symptoms severity was documented at T2. At both time points, parents reported more severe anxiety symptoms. Significant correlations between parents' and teachers' reports were noted for autism severity at T1 and T2, but not for inattention and anxiety symptoms severity. Conclusion: The study emphasizes the contribution of multiple perspectives for better collaboration between home and school environments. Obtaining accurate information from parents and teachers at the start of the school year may help to identify factors needed for better adjustment at school and to better address difficulties at home.