I think Grinity is talking about the other students that your DC would be working with when the school subject accelerates or grade-skips her. The children she is grouped with for instruction should be reading right around the same level she is, regardless of their nominal "grade". It might be better for your DC to be grouped with second or third graders who are also reading ahead and who are at her level, for example, than with sixth or seventh graders who might be reading below level.