If the person went from second to fifth, I read that as finishing second in the spring, skipping third and fourth, and starting fifth in the fall.
If you leave IQ out of the equation and just look at above level achievement scores, you can use the IAS to figure out what those would need to be (very approximately).
According to the IAS, an above-level assessment is at least two years above the current placement, so for a second grader, that would be a fourth grade assessment. Since this is a two grade skip, you would want to look at fifth grade norms.
The IAS says that a score between the 50th and 74th percentiles on the above level test is a "good indication of...readiness to learn new content." So, when looking at the 2015 norms for the MAP test (which are useful because mortals like me can actually see them all in one place), that would roughly equate to scoring between the 94th and 98th percentiles on reading and above the 98th percentile on math.
There is no way I'd skip a kid two grades based on that, by the way. And as the parent of a kid who actually did skip two grades, I want to add that acceleration is not necessarily all it's cracked up to be.
