[papagrit]

I know I'm a stick in the mud on this subject with the "real" football people on middle school weightlifting. I don't believe that a kid should overdo the weights until they are in high school and with a good responsible adult trainer overseeing the sessions when this age is reached. I feel lots of reps with lighter weights is the best course of training for a middle schooler. I raised two boys and both were strong as a pair of oxen naturally.
The reason for this opinion that I hold is the fact that my wife is a registered nurse who worked at Shriner's hospital for Crippled Children in Lexington for several years. Two of the most tragic, preventable injuries to children were: #1 Children that had been running around while their parents mowed or wanted to ride on the mower with their parents and them accidentally slipping in wet grass and sliding under the deck and #2 Kids that had been lifting too much weight slipping growth plates.
I had never considered this before she worked there, but, both accidents are way more common than most people would know. The growth plate on a growing kid is the soft middle of the bone that seperates and grows out toward the ends. When a kid lifts too much weight (What middle school boy doesn't want to put the key in the bottom of the universal weight set and show off to his buddies?) it can cause that growth plate to slide sideways and even with a minuscule slide they are done growing with that bone. Kids that have this happen to a leg bone on one side have to have the growth plate cut on the opposite leg so that one leg doesn't grow longer than the other. If this surgery doesn't occur fast enough and one leg grows longer than the other, then the growing leg bone growth plate is cut and the opposite leg is fixed up via surgery with an external fixator which is screws and rods that are placed through the bone on each end and have long screws that run parallel with the non growing bone. The growth plate is then intentionally broken and the fixator is screwed out a fraction of a turn every few days so bone can fill in the middle until the desired length is attained. It's like breaking the bone and letting the middle fill in a little with natural healing. A miserable and painful time for any kid.
Reps and light weights and training like some of the other have opined in here are the best ticket as far as I'm concerned. I wouldn't let my kids do the big weights in middle school. Drills and running with reps worked out best for them. They both went on to play college football as well and both were pretty decent players. Best of luck to you and make sure that kids enjoy what they are doing. Lots of sports at a young age allows them to settle into what they enjoy most when they reach the high school level. They can then decide if they want to concentrate more on particular sports. Make it fun!
Sorry for the book.