I think that my depends on the state. Does Common Core change this? My son was in a class that accelerated math by a year starting in 4th, but it wasn't until they were taking 'Pre-Algebra' in 6th that they took a different standardized state test than the rest of their peers. The schools don't mind since their grades were on average a lot higher than those who took the same class at the "regular time". Usually these test are a lower bound and a kid who is looking at grade skip would probably find they easy anyway.