Hmm, I don't know about that. Everyone I've talked to said, first of all, only put down jobs in med school or medically related jobs before med school, and second, there's no need to put down a reason for leaving if the dates are clearly stated as a summer job (eg, June 2000-August 2000). No PD is going to have trouble figuring that one out. All these entries are put into your ERAS CV, which you've probably seen; the PDs will quickly scan that rather than look at each entry in each box, and it's my impression that you want it to look like a CV you would type up yourself. All the CV books I've looked at (and other sources like Iserson's) agree with the above 2 recommendations. So I only listed one job, the one after my first year of med school, and didn't put a reason for leaving. The less they have to read (especially when an explanation is unnecessary), the better.