What is the optimum desk height for a kid's desk?

Setting aside the fact that kids come in different sizes, the desks that the schools get that they can adjust can be set for a to-top height of something over 20 inches to something under 30 inches.

If you're serious about the height thing, take a desk you are comfortable with and set a proportionate height for the child. If you park yourself in a "regular" chair and sit up straight at your desk, where does the top of the desk hit you? Just at the bottom of your sternum? Where ever it hits you, aim for that point on the child and measure it. The ergonomics will be similar. Good luck.

Also, See these charts:

google.com/books?id=9BM8Su0Oi00C&pg=PA11&lpg=PA11&dq=children%27s+furniture+sizes+height&source=bl&ots=KW7Uc0a_jX&sig=MHA7Ddqsq9V7KCyvPHA67rNPy3M&hl=en&ei=7tFhS-y0O4TosQOElsnCCw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CB4Q6AEwBQ#v=onepage&q=children%27s%20furniture%20sizes%20height&f=false">http://books.google.com/books?id=9BM8Su0Oi00C&pg=PA11&lpg=PA11&dq=children%27s+furniture+sizes+height&source=bl&ots=KW7Uc0a_jX&sig=MHA7Ddqsq9V7KCyvPHA67rNPy3M&hl=en&ei=7tFhS-y0O4TosQOElsnCCw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CB4Q6AEwBQ#v=onepage&q=children%27s%20furniture%20sizes%20height&f=false