I'd use Speer's low end or reduced recoil loads, with one of the available "single shot pistol" style bullets. They're designed to open at low impact velocity. When I used to make up plinking loads for my Encore pistol in 308, I used IMR 4198. 29.0 grains would be fine under a 125 or 130 grain bullet.
Check listed starting loads in a few manuals, if you want a little more velocity, but 29.0 grains of IMR 4198 will move the SSP 125-130 grain spitzer bullets fast enough to work out to 200 yards. If you sight in 3" high at 100 yards with that load, you'll only be an inch or so low at 200 yards. Hornady makes a 130 grain single shot pistol bullet that's designed to work at muzzle velocities in the 2000 fps range, which is where this load will put you.
When my dad started me shooting, my first rifle was also a .308 Winchester. Not being a reloader, and reduced recoil loads not being available at the time, he just set me up with a box of factory 180 grain loads. On behalf of kids' shoulders everywhere, I salute you for your quest to make your lad's practice sessions more comfortable.
