I personally believe that all rifles should wear glasses, unless you're looking for more of a challenge or hunting ranges so short that they're unappropriate, i.e. no longer than 75yrds. I personally would rather have a 2x42mm compact scout scope on a short range brush buster than open sights, but I don't really believe in taking running shots in thick cover.

As far as shooting with open sights being good training for marksmanship, I'm not a follower of that cult. To get the same groups with open sights as you do with a scope, yes, you do have to be a crack shot (or really poor shot with a scope), but I don't necessarily think open sights honestly teach anyone to shoot better. It's like teaching someone how to drive by plopping them down in a big rig, if he gets it figured out, he can drive almost anything, but why make it hard on them?

Giving them a scope allows them to focus on proper shooting position and technique, rather than focusing on fighting the open sights onto target. Once he learns how to shoot, he'll enjoy the challenge of open sights, and appreciate the advantage of the scope, instead of feeling like a scope is an easy cheat.

You should, of course, teach him how to shoot open sights as well, my dad gave me two BB-rifles on my 4th birthday, one with open sights and one with a scope, he'd made me shoot them equally by only letting me shoot one or the other at his choice (since he was a real father who controlled the guns and taught me proper gun handling)...I was then given a .22lr semiauto with NO sights for my 8th birthday (literally NO sights whatsoever) to teach me to appreciate sights, and learn to shoot rifles by feel and instinct. I still have that rifle, and I STILL shoot that rifle better than a new equivalent rifle with open sights.