I’ve seen this approach in both CME and also in the Discovering Algebra series. I like it as a concrete model for introducing solving equations. It also meshes well with using number tricks to approach algebraic expressions (which both of these curricula do as well).

Here are some resources for introducing solving equations via backtracking/undoing the steps:

- Dan Meyer has some good worksheets for both number tricks and undoing the steps in his Week 3 and Week 4 handouts (and slides).
- Discovering Algebra has worksheets and condensed lessons, with examples and stuff.
- CME Project’s worksheet on backtracking (and here’s the second, and here’s the third.)

Reminder: Things get awkward when you try to backtrack from expressions such as . For these, there’s no getting around observing that , but that needs to be done explicitly.

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