Classes at Hogwarts are taught in a variety of locations about the castle. Some, such as Charms, are taught in classrooms inside the castle. Others take place in the greenhouses (Herbology), in the dungeons (Potions), at the top of a tower (Astronomy), or even outside on the grounds (Flying and Care of Magical Creatures). A booming bell sounds throughout the castle and across the lawns to signal the end of class.

The classes vary in length, in content, and in approach. There are separate classes for each year and these are usually taught to groups from specific houses together. Some classes, however, are taught with larger groups of students from two houses. Some classes are "double," which seems to mean that they last twice as long as a normal class. Many classes have both a 'theory' portion and a 'practical' (or in U.S. parlance, 'lab') portion, so that the students gain hands-on experience in the subject.

The teachers vary tremendously in their skill as instructors and in their expertise. Many are among the most skilled in their fields, but there is considerable variation regarding their actual skill in leading their students to learn their subjects.

Some of the Hogwarts staff have first-class abilities both in their subject matter and in conveying it to their students. McGonagall, for example, is both a master of Transfiguration as one of the few Animagi of the twentieth century, and an excellent and even-handed teacher. Flitwick's good humor tends to lead one into overlooking that not only do his students learn his subject, but nearly all of them achieve a Charms O.W.L.

Some, however, like Snape, Hagrid, and Binns, are among the most skilled in their fields, but have distinct drawbacks when considered as teachers. In the case of the Potions Master, his treatment of his students overshadows his talents as a brewer of potions, while Hagrid tends to overlook the fact that most people lack his instincts (and let's face it, his massive physique) in dealing with the dangerous creatures that are his chief joy. Binns, to take another example, is so devoted to his subject that even death couldn't deflect him from its pursuit, and the only passion we've ever seen him display was on the subject of historical fact. Yet his lecturing style is ordinarily so deadly dull that even giant wars become monotonous in his hands, and students are so disengaged that asking a question in class is an event. (Even Hermione has only once spoken up in class to ask a question.)