We have Study Island and Brain Pop for free. I definitely would not pay for them. Study Island is way too basic and probably more geared toward remeial. Brain Pop can be fun but again very superficial.
My DS really enjoyed iCivics when he was 7 (2nd grade). Khan Academy has some appeal for both DS and DD when they were 8/9 (3rd/4th grade) as their subject matters are rather broad. Both DS and DD enjoyed Duolingo currently at 10 (5th grade). There is an Apple app for basic single digit 24, but it is not as fun or challenging as the real card game.
