If you like Calvin and Hobbes, you might like Frazz. Not because of any intentional influence -- the author even denies that he intended Frazz to look like a grown-up Calvin -- but there's a certain affinity.
Frazz is a songwriter who took the job of janitor at the school to make ends meet. Having had several hits, he no longer needs the money, but he loves the job. He also does mountain biking and has a tremendous crush on the first-grade teacher.
Several of the kids are repeating characters, but particularly the bright and bored Caulfield, who threw off the testing results by filling out his form with a Mona Lisa by dot, and other such tricks, and often ends up in detention despite being the sort who reads The Old Man and the Sea for fun and talks it over -- with Frazz, of course.
Various episodes. Including the time they accidentally took a class to see a farm and encouraged students to become farmers, vets, and vegetarians. The time someone brought a gerbil and didn't put the cage on a sturdy enough table. Eraser fights. And more.