The local high school here only has 4 classes during a day, and I'm pretty sure the teachers get a free class period. They at least got them when I attended. The teachers I know are some of the few great teachers you don't want to miss out on having. Such employees are almost always underpaid.
Lets stop talking about anecdotes, and look at some hard facts. The median compensation package for public teachers is $75k/yr (source) and they have a median of around 3 (maybe 4) years of experience (source). The BLS states that teachers are paid 11% higher than other professionals (source). At 53 hours/wk (source, it sounds like a lot of work, but it is 3 hours fewer than most professionals, even without considering vacation time (source). Considering vacation time, teachers who use all of their days of leave work an average of 171.5 days/yr vs 220 days/yr for private sector professionals with 10 years of experience (source), which isn't quite a fair comparison because professionals with 10 years of experience get more vacation than people with 3-4 years of experience.
If you multiply this out, most professionals are working over 1/3 more hours than teachers for 10% less pay. They generally get off of work early enough to make a dentist appointment, avoiding the need to shift hours around like other professionals, and their extra hours outside of the school day are free for scheduling as they see fit. Really good teachers might be working long hours for their money. However, when they're getting paid 50% more per hr, it's clear that most are not.
If you want to argue the difficulty and stress of a job, then that would be a different matter than I've discussed. It won't be fixed by reducing hours or increasing pay, but fixing polity.