because what's going to happen is if enough students are absent, there will be a big number of them who thought they would master the material no problem, would turn out to be wrong and then would bug the teacher incessantly to let them retake or do something to avoid bad grades. in most high schools in America or in many there are multiple difficulty courses, if your kid can master it no problem even when being absent, it is likely that this kid is not taking serious enough courses.