Will weight lifting at 12yo stunt someone's growth?

Define stunt growth?: No load training on the techniques of weight lifting are ok under the supervision of certified training professionals at 12, but load bearing is not. The growth plates at 12 are weaker than ligaments so fractures are more likely than ligament strains. This can lead to long term problems. The aap recomends children reach the last stage of puberty before full weight training (power lifts etc)

No: The key recommendation is to use light, 5-10 pounds or so, weights with multiple repetitions, always under adult supervision, for the best conditioning and strengthening at this age. Proper exercise cannot cause less growth than could have been expected without the exercise.