I have worn since puberty and it definitely takes some getting used to. Back then, they were REALLY thick and much easier to tell if they were in. Sometimes they would fold over, and you could actually see them up at the crease, and they would kind of sproing out at you .. that was a problem. They'd move around quite a lot until you got used to them.
Now that they are thin, it's hard.
So if you're looking .. here's what you do. You just have him look straight ahead, and move his eyeball left to right - not his head. You should be able (in natural bright light) to see the edge as it moves across his pupil.
I can't feel mine until around suppertime when they dry out (as you age) and then I have to take them out because they feel like sandpaper. But that's an age/dryness thing.
So he may not feel them at all - that's kind of the desired effect.
The other thing that may have happened is .. they can potentially get caught up around the corner of an eye. I don't think they can get behind an eyeball - at least not in my many years (I'm in my 50's) of wearing them since puberty. I have slept in them .. everything and the most mine have done, is sort of wriggled up to the corner and flipped around ...
That's very rare. Usually just if you really rub, or they dry out or you sleep in them.
Can he not look in his case to see if he put it in? I would suggest he have some system where once he puts it in, he flips his case over, or does something .. just so he knows he has done it, until he gets used to it. Like when one goes in, do this so you are sure ... then the next one ...
It DOES take a lot of getting used to - even adults find this very daunting. Everyone has to go in for an extra visit or so when starting out. Don't worry about it - this is kinda normal.
The thing to remember is, if he has left one in there, over time it WILL dry out and just kind of pop out on it's own - he'll feel it, rub his eye and it will suddenly feel squishy and kind of appear. It's not like it will just stay in there. Or if you did have two in there, same kind of thing would happen - one would dislodge the other, and one would pop out in the corner. You can't really screw it up.
I would avoid over rubbing etc - and I think leaving for now is best idea :)
** Added - they are really stick-to-your-eyes when fresh out of box, after a while they loose that suction quality, and are much easier to tell if in your eyes if that helps.
Also, you may be able to get them tinted (not so you can see color, or notice it). I'm not positive about that but I had some that were slightly blue for a while (it was a brand). You couldn't tell once in eye, but so much easier for handling. Maybe ask?
Good luck - he'll be an expert in no time. It becomes second nature very quickly