A schoolroom is a room used for teaching, especially in a small school. Think of one room in a village schoolhouse, with desks, a board, and the teacher at the front — sometimes the only teaching room the school has. In ordinary talk today we almost always say classroom. Schoolroom sounds a little old, or like a small country school; you will hear it in stories and in talk about the past more than on a modern timetable. Though actually, the meaning is close to classroom; the difference is mostly flavour, not a different kind of room.