I have an interview tomorrow. The principal has asked that I give a mini lesson (apx. 10 minutes) in either math or language arts for 3rd or 4th grade students. I am looking for ideas. Does anyone have an idea for something that would wow him?

Oh my, I wish I could help but my experience is in teaching high school English so it's very different. You could search the internet for ideas, but I'm sure you're already doing that. You definitely want it to be something where the kids are doing very hands-on kind of work, because they always love that. It needs to be fun, especially for that age, but it also needs to show your particular style or philosophy of teaching. Haha I'm not making this any easier or telling you anything you don't already know, am I? Good luck to you, though -- I'm sure you'll figure it out and do really well!

A friend of mine got a job teaching 5th grade recently. Her job interview lesson had to do with probability and M&M's. Definitely try to find something hands on if you go with a math lesson!!

My all time favorite lesson plan I did was math magic (and I really do believe math is magic!). There are all sorts of stuff on the web. I put a purple glittered wooden star on the end of a ruler and had a purple feather boa. I used the real picture overhead. As I recall I keyed my particular math trick to beginning algebra.
Another favorite math exercise I do with all my tutor students is making up times table games with playing cards. Kids love to make up rules and games and that really invests them in the whole process. I even ordered blank playing cards from magic houses.

Hope that might spark some ideas for you.

:-)