Alba asks the question, and Nancy thinks Mrs. Greenglass and all the other teachers must live in the school--but ""Oh no no no, she lives in a house just like we do,"" says Willie. So the three children take to watching Mrs. G's departures--by bus, on foot, by taxi, and then, puzzling them, in a friend's car that takes off in a different direction. Finally they ask her straight out, and the teacher not only confirms Alba's guess (""I live on the west side"") but also rewards the ""good detectives"" with treats from her latest ride, an ice cream truck driven by her uncle. Hoban's plum-colored city streets give a nice warm cast to the tame but true-to-life childhood intrigue, and her last picture reveals a secret the children haven't guessed: Mrs. Greenglass sits reading comfortably on the deck of her houseboat at the West 79th Street (N.Y.C.) pier.