The possible areas of growth within them are; speed, differentiating hundreds and thousands places (when dealing with money), flipping of numbers (50 vs 05), attention to detail of operation (+ vs -), and accuracy in calculation. He will also benefit from strategies to organize his work, as well as developing his ability to show his thinking in a written (non-verbal) format.”
Admittedly I'm one of those with strong math ability who tends to ignore relatively simplistic work showing and only ok processing speed, but I think that early elementary tends to over value mad minute type work. Not that it isn't important, but higher level math just doesn't require that sort of skill. There are computers for that sort of thing.
Those all seem like good things to work on, but I would also ask about growth beyond his strengths as well as the listed growth within those. I would want to be sure that what they are offering is what he needs rather than just being what they have available to offer, if that makes sense.
