Oh man this! I had a space cadet from hell my last year. So enthusiastic he would wait outside my grad classes to tell me he put the tupperware away. (Yay?) It got bad towards the end, but he couldn't take direction to save his life and nearly lost a finger doing the same stupid shit at least 3 times - even after telling him before and after to stay away from said danger.

Give him small tasks till you figure out what hes capable of and extend responsibilities from there. Explain everything you do as clearly as you would to your PI or another Grad cohort. He may not understand but take the time to explain, with my other lil minions this did a lot for their self esteem. Happy minions are productive minions. Acknowledge a work well done and when correcting something explain why "that" was not the best choice, because "A.B.C..." and thats why we do "This" because "A.B.C..." Let him sit in on the more technical stuff so he can learn. And like nadya_sparks said tell/show him how he contributed.

But most importantly (IMO) teach the kid how to take good notes. Show him the importance of good observation, critical thinking, and consistency.

Mentoring can be a lot of fun, just be yourself and treat them as competent adults. (P.s. i liked to show my gratitude by making my minions little presents for holidays. Like some candy on halloween, a small trinket for christmas..etc. doesn't have to be expensive, it'll mean alot that you thought of them)