Dianna, they may not actually be completely dry, or there may be impurities in the clay or most likely you may be bring the heat up too fast. That will usually be a problem at the first stage but it can cause problems at any stage.
If possible turn it on at the very lowest the night before you fire and then bring it up very very slowly. What kind and shape kiln are you using?

I was just going to say the same thing. If you don't put your stuff in completely dry or if you just put it in and then start the heating process, you will blow stuff up. When I run the kiln, I put the stuff in and then for a minimum of 10 to 12 hours, I let it just run on LOW with the lid cracked. Then I will close all vents and then turn it up slowly at first, step by step. SLOWSorry about the stuff blowing up, I bet the kids were disappointed. My first pottery teacher taught us a very, very special mantra.... NEVER NEVER fall in love with your pottery until it is completely done with all processes, as it can be ruined at any step along the way....

THis is so true and has happened to me many times. Even after having the pieces home... they have broken, my DD broke one once that was to be a gift and she cried she felt so bad. I laughed and said, don't worry about it... I can make another.

Really helps if you don't get too attached to stuff till it is done.

Oh yes I didn't mention cracking the lid. That could be important but I guess it wasn't so urgent after all. You are so right about not putting too many hopes in any one piece. I think we may have hit upon a rule that has a lot of application all over life.