In the schools in which I was, the best results were obtained by the students who were intelligent, but not too intelligent, because they were able to accomplish easily whatever was requested from them by the teachers and they were content with that, so they had good relationships with all teachers, resulting in uniformly good grades.

The students who were more intelligent than that, had difficulties, because they were frequently better than the teachers. Few teachers were OK with that, especially when the better students were unable to restrain themselves to not point at mistakes done by the teachers. Even when they avoided conflicts with the teachers about what is right and wrong, the better students were bored by what they were taught and they were reluctant to do various kinds of homework that seemed pointless for them. So they usually did not have good relationships with most teachers, with the exception of a few teachers, who either were very good themselves or they appreciated better talent when they saw it. So the best students had excellent grades only at one subject or two, with low grades at many others, so they ended only with average grades.