But, I'm running out of good puzzles that are good for kids. All the ones I can find are either variations on a theme, or are FAR too advanced for my kids. Does anybody have a good source for puzzles for upper elementary/middle school kids?

I don't know how many of these still work, but... Coolmath.com, http://www.coolmath.com, makes math fun for kids, parents, and educators—and is the brainchild of a college calculus professor. Figure This, http://www.figurethis.org, gives middle schoolers 80 printable math challenges with tips for parents and teachers. “When you back up from a wall mirror, do you see more of yourself?” FunBrain.com Numbers, http://www.funbrain.com/numbers.html, has original games based on sports and other fun things, designed to intrigue even math-resistant elementary school students.

The Wayside School series has a book of those puzzles where letters stand for numbers. The stories around them are hysterical, too.

I don't know that one! Do tell... How about Nathan Levy's Stories With Holes? Some of them are cheesy but there are a few that the kids love. I'm also a big fan of the logic grid puzzles for deductive reasoning skills. Mindware has some great books.

I just played it today with my tutoring student. You can play with one guesser or a whole class full of guessers. Giver (teacher) thinks of a 3-digit number. Guessers guess 3-digit numbers and giver responds with answers that give clues for future guesses. The responses are: Pico - means the guess has one correct digit, but it is in the wrong place Fermi - means that the guess has one correct digit, and it is in the right place Bagels - means the guess has zero correct digits Say my secret number is 123. The first guesser says, 350. My response would be 'P' for Pico (the digit 3 is in my number, but the guesser had it in the wrong place value position). The next guesser now knows that one of the digits (1,2 or 3) is in the mystery number. Say the next guess is 145. My response would be 'F' for Fermi. There is one digit correct (the 1) and it is in the right spot. The next guesser might choose 167. My response would be 'F' again - and guessers would assume the 1 was the correct digit. And so on and so forth. At first, kids think getting the response, 'Bagels' isn't a good thing, but you can remind them that it tells them which digits they never have to include again in their guesses, thereby narrowing the possibilities. What I love about this game is that you can see how the guessers are thinking, how their minds work.