In Massachusetts school calendars are set by cities. My city used to start the Wednesday after Labor Day but they switched that the year after dd16 started kindergarten. Now we start the Tuesday before Labor Day and get Friday/Monday off for Labor Day weekend. Last year with Labor Day being late they wanted to go back the last week of August but didn't have approval from the teacher's union. This year we went back August 30th and should get out around June 12th.
We have 4 quarters in school. In high school every two quarters is a semester. The vast majority of classes are full year but there are classes like gym and some art or business classes that are only half year. Depending on their class kids take either a midterm or final in Jan and June. They strongly discourage kids from taking more than 2 AP classes a year but in reality that is to help the kids who probably don't really belong in ap from taking all ap classes. My dd is doing dual enrollment so this year she started classes after Labor Day though the week before she helped with freshman orientation at high school plus had her college orientation (received her free textbooks).
We have 4 quarters in school. In high school every two quarters is a semester. The vast majority of classes are full year but there are classes like gym and some art or business classes that are only half year. Depending on their class kids take either a midterm or final in Jan and June. They strongly discourage kids from taking more than 2 AP classes a year but in reality that is to help the kids who probably don't really belong in ap from taking all ap classes. My dd is doing dual enrollment so this year she started classes after Labor Day though the week before she helped with freshman orientation at high school plus had her college orientation (received her free textbooks).