> They all mastered the material in "Introduction to Computer Science" in the semester.

There is no way all of them did. Eric Mazur tested this for people taking physics at Harvard, he found that even though every student got an A they didn't actually learn the material. He tested before and after on standard physics understanding, they didn't improve even though they got A in the class.

You can watch this video where he talks about it:

https://youtu.be/tn1DLFnbGOo?t=959

Teaching so that students actually learn the material is extremely hard.