From Peggy Kaye’s classic book Games for Math:
“Games put children in exactly the right frame of mind for learning difficult things.
“Children relax when they play — and they concentrate. They don’t mind repeating certain facts or procedures over and over, if repetition is part of the game.
“Children throw themselves into playing games the way they never throw themselves into filling out workbook pages.
“The games solidify the achievements of children who are already good at math, and they shore up children who need shoring up. They teach or reinforce many of the skills that a formal curriculum teaches, plus one skill that formal teaching sometimes leaves out — the skill of having fun with math, of thinking hard and enjoying it.
“If you play these games and your child learns only that hard mental effort can be fun, you will have taught something invaluable.”
Denise Gaskins' Let's Play Math 