This study examines Spanish secondary school teachers' views of gender differences in academic achievement and study choices. Thirty-six secondary school teachers participated in semi-structured interviews. Most teachers acknowledged that girls had better school performance, particularly in reading comprehension. Some were also acquainted with a higher predisposition to underachieve in boys. However, the teachers used different biology-centered arguments to explain these gender disparities. For many of the participants, that girls matured earlier than their male counterparts facilitates their adaptation to school demands. Likewise, a few teachers argued that the feminization of school favors girls' adjustment to school demands, whereas a number of them discussed that male adolescents do not consider school to be part of their gender identity. The usual attribution of intellectual abilities and effort to boys and girls was also discussed. In addition, socio-cultural and biological factors were accounted for gender differences in study choices.