I'd like to investigate the relation between pupil on task performance in classroom and their academic achievement. I found two old papers - Cobb, 1972; Michael & Davidson 1976. The both of them are not clear about the way they measured task performance though. Furthermore, Michael & Davidson partialled out the IQ. Do you think this is a good choice? In your opinion there's something else to partialled out in order to understand the relation between the two variables I choose?
And, how would you measure academic achievement (for example in Maths)?