My youngest is a bit like that. I mostly don't see him practicing anything. Last week at gym was a classic example. He couldn't do it, the more he was helped the more hopeless and giggly he became. The next time round there was no instructor at that station so he just breezed up and did it perfectly. I think he mostly co-operates with the teacher for assessment but I don't think he does as well as he van because he doesn't take risks.