Teachers were not under pressure to force every student to achieve an arbitrary target. Students were allowed to fail, so if they didn't want to work, there was no need to get into conflict over it. The way books looked and the quality of work in them was not scrunitised for the latest fads - again, less conflict potential.
Teachers were backed up by parents. If Jack didn't fall in line, he'd be in for a punishment at home as well as at school. Nowadays, parents back their kids up without even considering the other side (or the other 29 kids in the room). The responsibility for behaviour falls on the teacher, not the kids or parents.
Many school refusers were allowed to not go to school. Nowadays, there are teachers driving out in mini buses to pick them up and make them go to school, where they then spend every day disrupting.
Expulsions were an actual threat. Even a permanently excluded child has a way back in these days, and that is after a massive paper trail, often needing years' worth of evidence, before a permanent exclusion can take place. No way would a child "back in the day" have hit a teacher and be seen in the classroom again. In my school many years back, a kid in my class got excluded for merely telling a teacher to shut up. I can now get called a cunt on a daily basis and have the life of my family threatened without more than a detention happening (which won't be attended).
And finally, if a kid truanted, well, tough. We've wised up to what they might be up to, but back in the day, if they didn't attend, that was it. These days they can walk out of a lesson and be brought back 15mins later with me expected to catch them up on what the rest of the class did in that time.