As a homeschooler, I can vouch that an average homeschooler is much creative (and smarter) than the average non-homeschooler.

A few reasons why I think so:

When I quit school (age 11), I had the newfound freedom to study whatever I liked, beyond a few essential subejcts. I had no set schedules. I studied on Saturdays and Sundays, simply because I wanted to. There was no teacher around to say what I did was wrong (only the answer keys at the back of my work books!).

The last part is important - creativity will not be properly developed if you are afraid of being wrong. See this video (the speaker discusses the issue in the first ten minutes of the video) if you want to know what I mean: http://www.youtube.com/watch?v=RjwUn-aA0VY

Of course, we can't really blame schools because when you have 40 children sitting in the class, it's hard to let them to do what they want (very important to creativity!) and to give them individual attention.

Creativity, though, cannot be taught - it can only be encouraged. Individuals must develop it - and the main way is for them to find something they enjoy doing and apply all their effort at it. It may be mathematics, arts or sports.

Just look at Google with their 20% "innovation" time and see how it paid off. By letting their employees do whatever they wanted, Google got 50% of their products from there.

TLDR version -

Key to creativity: freedom.