e-assessment (f)or learning

As previously discussed, students aren’t great at giving correct units with their answers. However they have real probems with unit conversions!

The unit conversion shown on the left  is exceptionally badly answered, and a lot of students give up without even trying. The difficulties appear to stem from different aspects of the problem, as exemplified by the examples below.

First of all, let’s look at the problem students have in converting from one square (or cubic) unit to another, as on the right-hand side. Errors in this question fall into three basic categories:

(1) students who convert from km to m rather than from km^2 to m^2.

(2) students who do the converstion the wrong way round (i.e. convert from m^2 to km^2).

(3) students who do both of the above (i.e convert from m to km) – actually more common that just doing the conversion the wrong way round.

I’ve known for ages about the difficultly some people have in converting squared or cubic units. It fascinates me. (more…)