I'm just leaning about the YES tickets and think our son would love to do a class. When do they release the class dates for 2013? Do they usually have classes in Jan or Feb?
We attended a class this Janauary and I want to say the registration time opened in September. I would purchase as soon as they open up because some classes fill up rather quickly-"Wild by Nature" is an example. We initially wanted that one but I did not jump on it fast enough so we attended the "Synergy in Science" class (which was still good and very informative). Best advise is to keep watching this board for alerts that your time frame has opened up and make a bookmark of the Yes program class list so you can check it often. Good luck!
We went in January 2011. YES individual enrollment classes seem to start around mid-January through February. I assume your 4 yo will be 5 by then, and there are only a few classes open to kids that young. You will want to register as soon as possible. We will be watching for January classes, too. It's a wonderful program, and my older son really liked the Synergy in Science class last time.