I, too, value and encourage experimentation, and teach my students to allow
for some "mistakes" to happen...we can then both assign a grade to the
effort the student made (if the final product is a dog, but the student
tried something new and exciting), and to the end product. I work with
rubrics too...the students have a clear vision of what I expect from them.
What I'm happy about is the fact that they're beginning to extend
themselves. That's what it's all about.
I always said that if I could teach a child to be curious, I would have done
my job...and of course, our subject matter naturally leads to inquiry.