I see. Well, what can he do at the moment, with regard to explaining his reasoning? (On the IEP goal, this would be the "current performance level" section.) Can he state the problem/question? Identify what the end product should look like? Look at a problem and identify how he would set about solving the problem (using problems without actual numbers, to avoid the issue of just naming the answer)? To what extent can he do any part or whole of these?
Also, what level of mathematics is he working at? It would be easier to offer suggestions for IEP goals and objectives with that information. And this might sound a little crazy for someone at +3 SD in math, but has he had in-depth assessment in mathematics, not through a survey instrument like the WIAT, WJ, or KTEA, but through a diagnostic instrument, like the KeyMath-3? (Separates concepts, operations, and problem-solving strategies.) The standard scoring software for that actually generates suggested IEP goals and objectives, based on error analysis, which might at least start some conversations and balls rolling on the part of the school staff. The companion intervention manual has even more, also keyed to the error analysis.
http://www.pearsonclinical.com/psychology/products/100000649/keymath3-diagnostic-assessment.html
