That isn't true everywhere in the US. Our district has 185. Each state and/or district sets their own number of days.
The district I was working in, I worked 163 days with kids and had only 3 pupil free days per year. None of them were prepping the classroom though. They were all in-service days.
I'm in Colorado, our calendars go by hours not necessarily by the amount of school days. Elementary students need 968 hours, middle and high schoolers need to have 1080 hours. School districts generally need to have 160 school days in the calendar. However, we have a lot of rural school districts which have been allowed to maintain the hours required, but fewer school days because they use a four day school week to save on gas money for their buses.
Several other people mentioned teachers getting into school without a custodian. Again I'm in "what's a union?" Colorado, I have a key which allows me entry into the building and I do have a security code to enter as well. I did find out that there are some black-out hours when it comes to the key entry. I ran a ski trip and wanted to get into the building before 6am but they electronic key wouldn't let me.
I would LOVE that schedule!
It is nice once we get into it, but man is it hard right now saying that I have two more days of summer vacation.
We do get normal days off, PD, Labor Day, etc... but I won't list them all here
Aug. 2- first day of school- first quarter goes until Oct break
Oct. 9-22- October break- second quarter goes until Christmas break
Nov. 20-26- Thanksgiving break
Dec. 18-Jan 2- Christmas break
Third quarter goes until Spring break
March 19- April 1- Spring Break
Fourth quarter goes until the last day of school
Last day of school is the Friday before Memorial Day.