Speaking from experience, she generally brings home work every night (grading, lesson planning, etc). Weekends too. This fluctuates based on time of year (grading a round of research papers, preparing new lessons for a new quarter, etc).
Summers off? Kinda. New lessons and curriculums often have to be prepared for the following year. She's been doing that for a bit already whenever our little guy naps.
The other part of overlooked is the emotional toll. In my wife's case, she's dealing with high school freshmen, juniors, seniors, all who are one hell of a handful most of the time. Last year, she had a class that had her crying more than a few times. The kids were literally trying to make her cry.
But besides all that, teaching is a profession that is charged with preparing and educating our youth for tomorrow. Obviously, teachers go into it knowing this, and often for that very reason. But in my eyes, that's quite a responsibility. There are plenty of better paying jobs out there with less vacation that, at the end of the day, don't make much of a difference.
(For the record, my wife's district actually pays pretty well, so I don't think she's underpaid).