Our kids did elementary school from 8:30 am to 3 pm, with PE and two 20 minute recesses. The French cousins had school 8 am to 4 pm, no sports, and bilingual French/German. I do not know how that compares to the rest of Europe, though they were behind the German kids and expectations were higher when they moved there. In Germany they had shorter school days but much more homework.
My impression is that the US provides the longest…or one of the longest summer breaks compared with many other countries for its K-12 students.
When my daughter was in a British school she had 3 terms. The first started the day after our Labor Day, which was a bank holiday there. Then, in mid October she had a week off for half term. The first term ended right before Christmas. The second term started in January and went to mid February with another week break at half term. The second term ended about the first of April with a 2 week break. Then, the end of May was half term for the third term with school ending by mid July.
I really liked the schedule there. However, everyone went on holidays during the breaks so it was much more expensive to travel.
There is a movement in England to really come down hard on parents who take their children out of school to travel. The feeling is that there are enough breaks during the school year to preclude them from traveling during the school term.
I’m trying to recall what our term schedule was. The summer break was shorter than in the US: 8 weeks, roughly from mid/late July through mid/late September. The break at Christmas was longer than in the US–2 or 3 weeks, IIRC-- which facilitated travel. Thanks to the remnants of Empire–and BP 
--we had students whose families lived in places like Indonesia, Singapore, and Bahrain, as well as more routine European locations like Switzerland and France. I seem to recall some kind of week-long break in the spring.
BTW, I forgot to mention that we also had 4 or 5 classes on Saturday morning.