IMO a lever action repeater would be a better choice than a SA for young folks. It serves to teach them proper shooting technique.
I don't know why this would be, exactly. I mean, other than being able to more easily monitor chambered rounds while instructing, I don't know that the lever has any particular advantage over the semi-automatic in terms of shooting technique.
That's not denigrating the lever action, either. As I mentioned earlier, I have both of the rifles being talked about here, and I like both a great deal. The Marlin has actually eclipsed the 10/22 in terms of what I grab first to shoot, so it's not like I am just a Ruger fanboy (though, outside of this discussion, I kind of am). I just don't see why the 10/22 would be any worse at teaching proper technique is all.
Thinking about this, outside of just fun, I can tell you exactly the difference between these two rifles for me. The 39 gets broken out when I want to go hunting or am shooting more challenging targets, the 10/22 gets broken out when I want to plink or shoot tiny groups. It's particularly fun when I want to whack spinners as fast as I can, which is pretty darn fast! Incidentally, I have a scope on my Ruger, which obviously allows me to more precisely aim, hence the smaller groups.
EDIT TO ADD: Also, just to throw it out there, have you ever ran the lever on a Henry Golden Boy? I love my Marlin and won't sell it for love or money, but those Golden Boys are smooth, man. I would also add that if you ever happen to run across one of the admittedly ghastly looking Ruger lever actions, they have a very nice and short throw. I am convinced if they weren't so ugly they would be perennial best-sellers. I do not now, nor have I ever, particularly cared for the Winchester lever actions in .22 or anything else. I know they are iconic and all, and I have a pre-64 94 in .30-30 that is pretty nice, but I think the Marlins have always been a better rifle.