five
o'clock
`` We 're going to take a boy like George and study him till we think we know just what interests him most . And if in his case it 's animals , we 'll have a regular zoo in school . And for other boys we 'll have other things they really want to know about . And we 'll keep them until five o'clock -- when their mothers will have to drag them away . '' Her father looked bewildered . `` But arithmetic , my dear . '' `` You 'll find they 'll have learned their arithmetic without knowing it , '' Deborah answered .