Oh, also, for my daughter, it helped a little bit if the goodbye didn't come out of the blue. So, for example, I would say things like "after breakfast, Mommy will take you to school" then when we were getting her shoes/on we'd talk about how we had to get her shoes on so she could go to school. On the way there we talked (well, I talked) about who she would see at school and what they might do that day. Then of course, she'd start howling the minute we got in the room, anyway, but it still seemed like it helped a little bit that she was prepared! I'd say goodbye and tell her I'd see her that afternoon, walk out the door and hear her crying the minute I was out of sight.