Nowadays, teachers are regarded as key players in the process of identifying and catering to students' additional support needs within mainstream primary classrooms. However, teachers' professional judgements regarding students with special needs have been found to be contextually influenced (e.g. by school context, student population, level of achievement). It is unclear whether teachers' perceptions of their students' actual support needs are also influenced by their personal and professional characteristics. Hence, a better understanding of the value of teachers' perceptions regarding students' needs is needed. Therefore, this study explored perceptions of 109 Dutch mainstream primary teachers regarding four dimensions of students' additional support. It addressed whether these teacher-perceived students' needs are affected by teachers' years of experience, level of training, personality traits and self-efficacy beliefs. It was found that teachers' perceptions of students' needs were relatively unbiased by their personal and professional characteristics.