I remember reading a book about a young girl girl who falls for a boy who, I think, does magic. I would have read it between 1996 and 1999, but it may have been published quite a bit earlier than that. I think the cover was pink, and the (female) author's name might have started with an M, or her initials may even have been MM. I can't remember any details other than that the protagonist girls thinks at first the guy never noticed her, but then when she sees his bedroom for the first time, he has a picture of her up on the wall.

I finally figured it out by going to amazon-books-literature&fiction-authors a to z, and then browsing the "m"s until the correct one caught my eye! The name of the book is The Changeover and it was written by Margaret Mahy.