I agree with Dude that I would ask about the pace of instruction, but also whether individual students learn as a group or whether they are allowed to learn at their own pace. That is, if your DS needs to move faster in math, for example, possibly faster than the "middle range" of the gifted group - will they differentiate for him? Or are all TAG students instructed at the same pace?
We failed to ask this question about our school's programming beforehand, and although the G&T programming is far better pace than the general ed pace, it is often still too slow. So we have learned the hard way that G&T itself is only part of the solution.