Anything that gets kids shooting more is great, and this will definitely tame recoil. Don't neglect taking a caliber more suited for your boys tolerance and encourage shooting without the aid of a rest. While pinpoint accuracy from the bench does much to encourage a young lad, it's time spent shooting off hand that will benefit him in the woods.
Simon, you make many good points. Another option is to load down with appropriate bullets. I started step daughters with 7 08 load to 2300fps and single shot pistol bullets. They had same point of aim at 100 yds as full loads within an inch. Killed deer great, very minimal recoil. I had them shoot a shot from a field position for every shot they shot off a bench.
I have one I use some, but did find that with my Ruger No 1 it would not group on the lead sled. It wouldn't let the gun do what the harmonics want to. Off the sled the gun would group 3/4 MOA, on the weighted sled it was all over the place.