We don't actually know that this is true since we're never shown a timetable or given a full list of subjects that they have. Hermione tells Ron and Harry that they've got to keep all their old subjects when they choose new ones in Chamber. Since Hermione hates flying and you can't learn how from a book, I doubt that she considers flying lessons a subject at all and they are dropped at the end of the second year to make room for the new subjects. So possibly Madam Hooch teaches the first and second years how to fly. We only ever get to see one flying lesson, in which she doesn't actually get to teach them very much, but I reckon she must be a good teacher to still be knocking around Hogwarts.