There are tons of math, games, science, chemistry, etc. upper grade apps for the iPad. Finding uses for the primary grades seems a bit more difficult. Please keep in mind that I have not taken the time to explore this as much as other iPad education users have. Below are a couple of uses.
Children’s books – There is huge possibility here! Unlike the Kindle, the iPad is colorful and gives the impression of actually turning pages. Children learning to read need to have their hands on authentic books. I have a 4 year old who LOVES books but when I put the iPad in her hands she wants to watch videos. Here is a screen shot of one children’s book I found in the iBook store: