Slughorn combines a Potions assignment with Professor Sprout for Herbology. It's a partnership assignment for students taking both NEWT classes and that doesn't involve very many. Last term, Hermione was surprised that Malfoy was; he'd seemed quite disinterested but evidently his parents are making him carry onward with his studies. Once she thought about it, no matter his level of motivation, of course his father would force him into it. He's taking as many NEWT classes as she is - one of the few who is.