One of the best ways to catch errors is to ask what the answer should roughly look like before calculating.
Estimation is not a weaker version of math. It is a way to keep arithmetic connected to meaning.
Teaching Move
Before students solve, ask:
- Should the answer be bigger or smaller than 1?
- Is it closer to 10, 100, or 1000?
- What would a ridiculous answer look like?
Example
If a student gets 900 miles per hour for a school bus speed, the issue is not only arithmetic. The issue is that the number was never checked against reality.
COSMO Challenge
Give students five messy-looking numerical expressions. They must estimate each one first, then calculate.