The game-board is a 4x5 grid of stickers (I used 4 each of 5 different images) placed randomly. You could also make a larger board and leave some spaces blank, or make more/different shapes - I just made this up as I went along. For the puzzle challenges I stuck one of each sticker image onto strips of laminated paper and then used a dry-erase marker to make up the challenges as I went along based on what I saw from my kids' abilities (you could make an entire booklet of challenges from easy to hard). I specifically chose to use dry erase markers for the challenge strips so that my kids could make up their own puzzles and then count how many of each type of image is showing to fill in the challenge cards themselves (and try to stump Mommy).
The rules of the game are simple - use the tetronimo pieces to cover the stickers until only the required number and type of stickers (from the yellow challenge cards) are shown. My kids loved the "Peek-a-Boo" aspect of the game.
There may be different solutions to a single problem (especially if a lot of stickers are revealed). Older (high school) students could do an interesting Math Circle study on this game and the mathematics of arranging the stickers on the board to limit the number of possible solutions, etc..
So how did my 3-year old kids do?
We have a number of other Tetris-style manipulatives/games around the house, so my girls are already familiar with how these shapes fit together. They exceeded my expectations and quickly understood how to play the game. They didn't play off the challenge cards, but I would point to a sticker and say, "let's try to see if we can hide all the other stickers so only this one is playing peek-a-boo" or" let's see if we can get only the flower stickers to show", etc.. and they got the concept of how to work around the stickers that were supposed to be showing and try to get the others covered. Best of all, they enjoyed playing, so this homemade game is definitely a winner - and something that my kids can grow into as their logic and spatial reasoning skills continue to improve.
It's a fairly simple concept, but there is something about this brain puzzle that was strangely addictive, and I couldn't keep my hands off it either, playing with different ways of placing the pieces and making up challenges for myself. Who would have thought that colored paper and some stickers could produce an activity that's fun for grown-ups too!
UPDATE: I was so inspired by how much my kids enjoyed early math "games" that I created the La La Logic Critical Thinking Curriculum for 3-6 year olds, which includes online brain challenge games, printable worksheets, enrichment activities and more!