I think this is no different than the situation with programmers. Are most programmers "overworked" in that they get too much done? No. But many are "overworked" in that they are constantly distracted with little problems and don't protect enough time to think hard about any single issue. As a result, they do lots of short-sighted work and don't get enough done overall, but also feel constantly busy and hard-working.

I think that's pretty close to what normal high school is like today. There are constant distractions for standardized testing, mandatory this-and-that, worry about your SAT scores, etc. And not enough sitting down to understand what this novel is really about. Or what an integral really is.

I think this explains both the subjective feeling that students are "overworked" and the objective truth that they aren't doing or learning nearly as much as was traditionally expected of students.