Subject: Can you tell me a scientific principle for what makes rock candy form?

My son is making Rock Candy for a science project at school; and we have 
to know why it forms the way it does.  We have checked the internet for 
hours and the only explanation we could find was a very complex one at 
your web site.  Can you tell me where to look, or tell me why yourself, in 
language that a second grader can understand, as he will have to explain 
it to his class. Thanks.  I hope you can help.

Re: Can you tell me a scientific principle for what makes rock candy form?