RAD - weight training for kids

In reading through RAD's old posts (many of which I thought were excellent) I saw where he said that at age 11 or so kids are first able to start lifting weights. I would appreciate any advice on the subject of children and weight training, or any articles anyone can point me to. I have spoken to Paul Nyman at Setpro, (of whom RAD has spoken highly) and he does not agree with the above view, but believes that certain weight training can be beneficial to younger children(at least as far as using up to 50 or 60% of a child's one repetition max). Thanks for any info you have.