My kid often refuses to show what he knows. He will tell us that school is boring, so we remind him that the only way the teachers will know what he can do is to show them. He is very sensitive to random adults quizzing him, but he is OK with the teachers doing it in appropriate situations. They all admit that they probably don't really know what he can do, but they have a decent idea.
I would try talking to your son about what he wants, how he feels about school, and the reasons he needs to show the teachers exactly what he can do. We only did a one year acceleration for our son in reading only, and in class individualization for math. He could have done a two year acceleration in both reading and math, but none of us wanted to do that. Socially, emotionally and work production/stamina and attention, behavior, etc were not sufficient for a two grade acceleration as a kindergartener.
