Some teachers are nice and give you a 5-10 minute break halfway through the lesson, others don't. Luckily I enjoy learning and am able to quite easily make it through lessons. (also probably helps some people prepare for 3 hour HSC exams as you already have to focus for 2 so you're 3/4 of the way there)
We definitely have some lessons where we're productive for like an hour and then devolve into talking so loudly amongst each other that the teacher a room over has to come and ask us to be quiet. The only other thing that's good for 2 hour periods is having a free period in the morning or afternoon. The school allows for a flexible timetable so you can leave at 1pm on a day you have a free in the afternoon when usually you would end at 4pm. Some people don't even have to come to school on friday because of having 2 free's in the morning (friday ends at 1pm)