Search "chess endgame training" in the app store on your son's iPad. There are a couple of free ones: Chess Endgame Trainer and Swift Chess: Endgame Puzzles. I haven't tried them so can't give a recommendation.
There's also a good free app for tactics that I use: ChessTacticsPro.
Congrats to your son for his achievement in chess so far. Quite impressive.
Coming back to this thread -- I think the chess,com endgame drills are not that well organized or modular yet. The best I've seen on Ipad is the ChessKing Total Endings app.
You son would be better served by using a real board and pieces when studying.
IMBacon: agree - he does play endgames with his coach OTB, But frankly, he is so busy (I know, it's harder to be an 8 year old than it was when I was that age) with sports and school he has to squeeze chess in on car rides, at the airport, etc. Having a good Ipad app is key, or else he will literally not do any chess in those windows. BTW, I just ran his games from the last tourney through the chess.com analyzer - his final game was his cleanest ever: 55 excellent, 2 good moves. I am sure it is a large part luck,but it's definitely the first one he's played OTB with no inaccuracies . . .
This is my son's account. He is in 2nd grade and rated about 1400 USCF. Yesterday he drew a won endgame, and lost 2 other from equal positions. 2 were rook + many pawns, another was K + pawns, with some doubled pawns. The other kids were older, and just seemed to have more experience with such situations, and it showed.
Anyhow, he needs some more practice drilling asap. He uses his Ipad to practice (not the PC). What would people advise as the immediate next step? Here is what I have been suggested so far:
1. ChessKing Endgames drills
2. Chessimo
3. Silman book in ebook format for Ipad
4. Chess.com - just do all the endgame drills, then revisit the topic.
Thanks.