Great topic! Here are a few more:

Just because an early elem. kid can only write at age-level, that should not keep him from doing math 2 or 3 grade levels ahead.

Kids who know 80-90% of the curriculum before a unit starts should not have to sit through that unit. Please accelerate this kid (unit/subject/whole grade, as applicable). Even if there are gaps, when my kid encounters such gaps in later units, a quick teaching of this will cover it.

Just because my kid sits quietly through class all day long and appears to be happy is not necessarily indicative of a kid who is appropriately challenged by the material being taught. (Says the mother of a child who told her that he loves easy things he already knows, because that leaves more time for his preferred activity of daydreaming.)