going back to an old job?

so i left my old job 7 months ago, too impulsively, i now realize, for one i thought would be better but which has turned out to be far, far worse. i left on good terms, am still in touch with my old boss, and have a fairly good sense that she'd be willing to have me work for her again. more important, i decided over the last few months that i'll be applying to grad school this fall, and the old job, it turns out, is much more closely related to what i'll be studying than my current one. the schedule is also far more flexible, which would give me ample time to work on my application, take exams, etc.

so do i try to go back to the old job? has anyone done anything like this? i seem to have more or less talked myself into this already, but part of me worries that it may look bad in the future, be perceived as failure in some way or something.

oh, and the fact that with grad school coming up, i'd only stay some 1.5 years isn't a huge problem. there's a good deal of turnover at this place, with year-long or even semester-long contracts - and i'd obviously be upfront with them about my plans...