My DD sort of skipped third grade math and what has tripped her up a little bit is not calculation stuff but things like weights and measures (what's bigger, a pint or a quart?), the metric system, etc, which cannot be faked based on good number sense and require a little more time to get cemented. Also, concepts like perimeter and area, congruence, etc. All these can be taught quite easily but are going to be met with a completely blank look if she's never encountered them (whereas a bright kid is going to be able to figure out a lot of other stuff by herself).
