Background: Student's temperament plays a significant role in teacher's perception of the student's learning style, educational competence (EC), and teachability. Hence, temperament contributes to student's academic achievement and teacher's subjective ratings of school grades. However, little is known about the effect of gender and teacher's age on this association. Aims: We examined the effect of teacher's and student's gender and teacher's age on teacher-perceived temperament, EC, and teachability, and whether there is significant same gender or different gender association between teachers and students in this relationship. Sample: The participants were population-based sample of 3,212 Finnish adolescents (M = 15.1 years) and 221 subject teachers. Methods: Temperament was assessed with Temperament Assessment Battery for Children-Revised and Revised Dimensions of Temperament Survey batteries and EC with three subscales covering Cognitive ability, Motivation, and Maturity. Data were analyzed with multi-level modelling. Results: Teachers perceived boys' temperament and EC more negatively than girls'. However, the differences between boys and girls were not as large when perceived by male teachers, as they were when perceived by female teachers. Males perceived boys more positively and more capable in EC and teachability than females. They were also stricter regarding their perceptions of girls' traits. With increasing age, males perceived boys' inhibition as higher and mood lower. Generally, the older the teacher, the more mature he/she perceived the student. Conclusions: Teachers' ratings varied systematically by their gender and age, and by students' gender. This bias may have an effect on school grades and needs be taken into consideration in teacher education.