It would make sense that chess would improve the intelligence of the players. There is a lot that goes into playing the game. Not only do you have to remember how each different piece works, but you have to keep up with where your opponent is and where they might go in the future. It takes forethought and planning to survive a good game of chess.
There is also a lot of discipline to playing chess. It is not a game that is over quickly. It will take patience and endurance. Both of these are great skills for kids of all ages to develop.
Chess is a fun (and quite) activity that every person should be able to participate in at one lever or another. It may not make them smarter, but it is likely to help them understand that actions have consequences – even if it is just a game.