At out local public lower school in CA, every Tuesday, the students get out at 12:00 noon. The other days, they get out at 1:45 pm. The school also has a number of "special days", where they get out 12:00 noon also.
We did the math and figured the grades 1-5 students miss out on a full year of schooling during the time at this school...all due to these unbelievable hours. It appears the schools were given the minimum days that they had to teach and decided to make those days shorter.
You are correct. My wife, a teacher, had to teach 180 days per year but she also had to be at the school for an additional 20 "teacher work days". That's a grand total of 40 weeks, or 10 months, per year. Teachers had the option of getting their pay in 10 monthly checks or, if they wanted their pay to be annualized, 12 monthly checks.