We're going to go through the same thing in 2 weeks, my daughter will be in 1st grade and my 4 year old son is home with me. We still haven't decided whether to do pre-K with him, I don't really think he needs it except for the socializing aspect. I plan to try and keep him quite busy, but it's never enough. We'll take walks and bike rides and do "school" and go to the library and of course whatever shopping I need to do. I agree not to let him get away with throwing fits, the same rules apply as before sister went to school. Sending him to cool off is great. I think he'll get the idea but it might take a couple days. Hang in there!!!