Diagnostics of autism spectrum disorders (ASD) includes assessment of child’s spontaneous behavior. Although diagnostic criteria for ASD do exist, there is a great amount of subjectivity in their interpretation. Many behaviors that are seen in children with ASD can also be identified in children with typical development. However, in children with typical development, the frequency of these behaviors is decreasing as they age. Therefore, they could be more easily detected and are considered to be more atypical. The objective of this study is to examine how different people assess spontaneous behavior of five-year-old children in view of what is considered typical for that age and to explore possible causes of differences in their assessment. For this purpose, an electronic questionnaire has been developed, which includes examples of stereotypical and restricted behavior, as well as examples of deficits in social communication and interaction, designed according to diagnostic criteria in the Diagnostic and Statistical Manual for Mental Disorders (DSM-5, 2013). The sample consisted of 205 adults, divided into groups depending on their age (18-30 years old; 30 years and older), types of occupations (professionals specialized for developmental difficulties - speech therapists, psychologists, rehabilitators; professionals who most of the time work with children with typical development – preschool or school teachers, pedagogue; others), and whether they are parents or not. The results have shown that there are statistically significant differences in assessment within each group. Young adults more often feel that behaviors such as the desire to watch the same cartoon episode repeatedly, interest in car brands, not having a best friend and rare imitation of other children, are atypical. Almost all described behaviors are more often perceived as atypical by professionals specialized for developmental difficulties than by those professionals who most of the time work with children with typical development and by other professions. Unlike those who have children, adults who don’t have them more often consider that interest in car brands and numbers, as well as not having a best friend and rare imitation of other children, are unusual, while interest in electronic device is seen as more common. Due to the large difference in the number of male and female participants, as well as in the number of parents of children with developmental difficulties and parents of children without them, the differences in assessment between these groups were observed only at the level of descriptive statistics, where it is apparent that men and parents of the children without developmental difficulties, are more likely to treat described behaviors as typical. The obtained data suggests that the assessment of children’s spontaneous behavior depends on the experience that adults have with both children with typical development and those with developmental difficulties, as well as on the level of knowledge of (a)typical child development.