In high school I never skipped school, did well in grades. Freshman year of college, never skipped school, had awesome grades. Sophomore year of college, skipped a few, grades declined a tad. Junior year of college, skipped a lot of classes, grades were pretty good (because of how the classes grading structure were made.) Senior year of college (what I'm at currently,) never skipped a single class (except for field training,) and I've gotten phenomenal grades (due to the fact, I'm there and I am taking classes that I want to take, not college requisite classes.)
So. It's okay to skip every once in a while. But keep abreast of your work, don't fall behind, because it's next to impossible to catch up depending on the class.