When looking for answers to the question of academic (non)achievement of regular pupils and pupils with special needs, it is necessary to take into account the extraordinary complexity of factors, ranging from psychological across instructional to home environment variables. The academic achievement is not only a reflection of the pupil's knowledge, but is also influenced by the pupil's behaviour, the teacher's expectations and finally the relationship established between the teacher and the pupil. This paper contributes answers to the question which of the traits, perceived by teachers, explain the academic achievements of regular pupils and pupils with special needs. Our analysis shows that perceived traits that explain the academic achievement of regular pupils refer to academic as well as social behaviour, disruptive behaviour and self-regulatory behaviour; therefore, they cover all areas of perceived traits we studied. In pupils with special needs as a whole and in particular groups of pupils with special needs, the factor which presents disruptive social behaviour proved as insignificant, which consequently means that the academic achievement of pupils with special needs depends more on academic and self-regulatory behaviour, task activity and social inclusion.