You're joking right?
A forty hour work week ends up being about 2000 hours in a year.
Here, teachers get ~2 months off in the summer, ~1 week at spring break, and ~1 week at Christmas. Nevermind weekends, regular holidays, field trips, etc. Here also, afaik, they can choose to take their 2 month vacation pay during the ~10 month work year, or to have it deferred so they have an income during the summer months(Heard this from my uncle who's a teacher).
In the end, that's the price they pay for the job they have. They do a years work in ~10 months time, and are paid for a years work.
Khan academy has an idea of the learning of new material being done at home, while the practice is done in the class room where the teacher can help the student troubleshoot any problems they're having difficulty with, instead of parents working 'X' hour days, and either being 'too tired'(poor excuse IMO), or just simply not knowing how to solve the problems. Again, IME, was that the new material was taught in the classroom, then practiced at home, and the next day something new was to be learned. It was a little too fast for me when learning pre-calculus and physics in high school. I do feel that the above mentioned way would result in higher grades and understanding of the material.
I do feel that good teachers, which I have only encountered a handful of(the kind that teach to the student, not the class), are grossly underpaid for the impact they can have on many people's lives.
On the other hand though, IME, is the curriculum needs to be readjusted. Too much time is wasted in k-12.
There's no reason algebra, critical thinking, life skills, and others shouldn't be taught at a young age, as this is when these important(in different degrees) skills can be made into lifelong habits.
High school would be better spent moving in the direction of a certain field of interest, with electives kept in mind in case that field doesn't feel right later on. Sort of like a block system where everyone has the same base, and each one branches off to a certain field(like a tree if you'd like a graphic representation).