➗ Math apps and platforms · 🏫 Classroom tools
Which One Doesn't Belong?
By Mary Bourassa and contributors; now hosted by Christopher Danielson (Talking Math with Your Kids). Visit Which One Doesn't Belong?
Desk research from the maker's own pages. Not yet tried by us. Checked 2026-10-24.
Which One Doesn't Belong? is a free online collection of math puzzles. Each set shows four pictures, such as shapes, numbers, graphs, expressions or photos, chosen so that any one of the four could be the odd one out. Children pick one and explain why, and there is no single right answer, so the point is reasoning and talk. Teachers use it as a class warm-up; parents can use it at the kitchen table. Teachers contributed most of the sets.
Our take: A free, proven classroom routine that also works at home for any age; just bookmark the new Talking Math with Your Kids address, not wodb.ca.
| Ages it suits | about 4-18 (sets range from preschool shapes to calculus graphs) |
|---|---|
| What its terms say about age | No terms or age rule posted; no account needed to view the sets. (terms) |
| Price | Free. Free online sets (Oct 2026); a related picture book and teacher guide are sold separately. |
| Works on | Web |
| Account | No account needed |
| Ads | None |
| In-app purchases | None |
| The AI in it | No AI. |
What's good
- Free, no sign-up
- Every answer can be right if explained
- Spans preschool to high school
- Great for family math talk
Watch for
- The old address, wodb.ca, is now a parked domain for sale with ad scripts; use the new link
- No privacy policy on the host site
- Tracking scripts on the host site
- Needs an adult to lead the conversation
Data and privacy
Not stated: the host site has no privacy policy link. It shows a cookie notice and loads Google, Facebook and WordPress (Jetpack) tracking scripts. Read the privacy policy.
Does it work?
A widely used teacher routine with many teacher write-ups; no independent study of the website was found.
In the Big Index
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Where these facts come from
- https://wodb.ca/
- https://talkingmathwithkids.com/?p=146583
- https://talkingmathwithkids.com/wodb-about/
- https://talkingmathwithkids.com/wodb-shapes/
- https://talkingmathwithkids.com/
Prices, terms and features change. Nobody paid to be listed, nothing here is an affiliate link, and Peabody never rates itself. Where we and the maker disagree, the maker's own pages are the ones to trust.