Ok, you gave your daughter instruction and she no longer plays the game. Maybe there's cause and effect there, or maybe she just gave up the game because she didn't want to play anymore. I think it's quite a leap to presume that if you do the opposite (no instruction) your second child will want to continue playing. It's also possible that years of incorrect technique will be impossible to fix at 13 years old, or will put the kid hopelessly behind his peer group and make getting onto a competitive team at that age very difficult. I guess you'll find out in 10 or 15 years. Reminds me a bit of Whole Language though.