My son is in first grade and is a great reader. While reading comes naturally to him, math does not. He is getting along fine, but when I saw this game, labeled for first through fourth grade, I thought it might give him extra practice and more ease with math while being disguised as a DS game.
I have spent a little time with him trying this game out today. While I didn't want to help him too much so I don't skew his results in the game, I could see right away that this is certainly not for a first grader. In the Exercises section under addition at the easiest level, he was asked to add 20 + 38. In his head. I quickly went over some of the other activities but all were clearly way out of the range of a first grader.
I think this can be a great learning tool for the proper age group, I am just not sure what age that would be. Maybe it would be more appropriate to start around fourth grade for easy. Take this into consideration before buying as the age recommendation is so out of range.