epoh, Singapore Math has some assessments available on their website http://www.singaporemath.com/Placement_s/12.htm

that might be of interest to you.

And, yes, kids this age are not that tactful! lol So maybe he asked at the wrong time. But he did ask and I do think the teacher should be responsive to that. Maybe you could work it out where he does some additional material that you provide instead of some of the practice sheets that he would otherwise be doing at school. Flash Kids' Math for the Gifted Student series is a workbook alternative that doesn't move beyond the grade level curriculum but instead provides more complicated and thought provoking exercises.

I don't know if they would go for that, but even if you did something along those lines at home you could be feeding his math needs without sending him way ahead in the curriculum.