33 subjects, ages 12-16. If one wanted to cook a research design related to IQ and brain changes, you couldn't do much better than straddling puberty with your testing. Considering IQ is age normed, and the brain does change through puberty, nice. It's probably a better argument that kids develop at different rates and that intelligence+maturation has a relation to brain structures than it is to conclude that intelligence is generally volatile.

And on the other side of head scratching is the professor suggesting that IQ changes are related to school learning in the context of an age-normed test amongst kids assorted into school in age cohorts.