Ideally the first day on call with the med student (assuming you two are always on call together and he isn't being swapped between interns) when you have the time and if the service isn't at 150% capacity, go down to the ER together, make him do the H&P without seeing you do it first, and then do your own right then and there with him present so he sees what he missed.
Take time afterward to talk about his H&P, give feedback on how to make it more structured/systematic/thorough/whatever, and then have him write it up (he probably has to write it up anyway for his clerkship, or at least he'll need something handy to read off of for presenting to the attending at rounds the next day). His presentation skills will be terrible if this is his first rotation (everyone's are, and no one sticks to the right format), so make him do that presentation for you at least twice the first night, if you have time. From here on out, whenever possible, have him go see the patients first for admission H&P's, unless absolutely necessary. After a few, you don't need to be physically in the room anymore, and he doesn't need to watch you (unless he's doing poorly and needs the extra remediation). But always compare notes afterwards, to make sure that he asked all the pertinent questions and found all the pertinent findings that you did--he won't have, and that's the point.
Check his H&P writeup to make sure that it's written appropriately--your goal, if your hospital allows it, is to have him do the *entire* H&P and progress notes for all of his patients with you just annotating here and there and then countersigning. Obviously, this won't happen until several weeks into the clerkship, when he finally learns how to write an H&P or progress note that's marginally usable. By the end, you want him functioning as a sub-sub-intern, taking full responsibility for his clutch of 2-3 patients or whatever, and not just following you around like he's job shadowing. (check with him/his syllabus/the clerkship director/other interns/the resident to find out how many he's supposed to carry or admit per call night).
Obviously repeat the same thing with the daily progress notes. Be a stickler on progress note quality--just keep asking yourself if what he wrote as a note would be acceptable if you just countersigned it without further modification. If it's just a knowledge thing, this is a quick 1 minute teaching opportunity. If it's a note structure / incompleteness / messiness / incoherence thing, be harsh on the note, but not on the student. He'll thank you for it later, unless he's a complete idiot. My first intern on medicine told me not to write notes, since it was faster for him to do it himself. I thought he was the coolest dude at the time because of that, and because he sent me home at like 3 every day. In retrospect, he was my worst intern, because i didn't learn how to function independently until later in the clerkship.
Good luck with your little penguins...