Ask how and why
The best test of whether students can get answers right consistently is whether they can explain how they got the answer.
Teacher: How far is it from Durango to Pueblo?
Student: Six hundred miles
Teacher: How’d you get that?
Student: By measuring three inches on the map and adding two hundred plus two hundred plus two hundred.
Teacher: How’d you know to use two hundred miles for each inch?
Student: I looked at the scale in the map key.