No. It could be that girls on average score better at whatever makes you do good in teacher exams - things like verbal ability, agreeableness, ... - whereas boy

No. It could be that girls on average score better at whatever makes you do good in teacher exams - things like verbal ability, agreeableness, ... - whereas boys score better (or just the same) on the actual subject matter. The difference could very well be biological (although some would call that "structural sexism" as well).