After taking Chem20A, I thought this class was almost a joke! The material is much easier, because it's less conceptual than 20A. The class was not that difficult at all, but then again, I wouldn't say that it's an easy A either. He's very straight forward with his HW and most of his midterm questions. As long as you do the HW, you'll do fine. He doesn't go by the physical science book that we have. Instead, he uses the Chem14B book, and their problems are easier! I never read the book, but I managed to get good grades on the quizes and midterms. I have to admit, the final was unexpectedly really harder than his midterms. Overall, Lavelle is a good prof. He explains the concepts clearly. He'll answer all the questions you may have and he won't make you feel stupid for asking them, unlike some profs. I don't know why people say he's a bad lecturer. I don't think he's bad at all. He may not be the most exciting, but he's not the worst either.