For grown-ups
SortWalkPals is a sorting network, a famous idea in computer science, small enough to chalk on the pavement. Six lanes and twelve boxes. In each box, the two toys that meet compare sizes, and the smaller steps to the upper lane. Whatever order they start in, they walk out smallest to biggest.
At each box your child guesses: will they swap? Then they rub out one box and see a mix that now comes out wrong. Every box in this plan matters. That is checked by trying every possible mix, so the app is never guessing.
Then print the chalk plan, draw it outside, and walk it with six toys or six people. It is the same idea used inside fast computers.
What it never does
- No accounts, no ads, no tracking — anything kept stays on this device.
- No streaks, timers to beat, points to chase or leaderboards.
- No chat, and nothing anyone types is sent anywhere.