Yes, we use the word "class" but it just refers to the group of children to which a child is allocated (or to a group of children studying a specific subject for an hour or so). At my secondary school, there were six classes of 30 children in each year.
Second year (age 12-13) - 6 classes of 30 (180 kids)
Third year (age 13-14) - 6 classes of 30 (180 kids)
Fourth year (age 14-15) - 6 classes of 30 (180 kids)
Fifth year (age 15-16) - 6 classes of 30 (180 kids)
So there were 30 kids in each class, 180 kids in each year, and 720 kids at the school in total.
As far as the other meaning is concerned, we had about five classes a day - 1 before morning break, 2 before lunch and 2 after lunch. Each class lasted about an hour.
Each morning, each class of 30 met in their "form room" (the individual classroom to which that class was allocated) for about 15 minutes at 8.45am - the teacher took the register (to see who was at school that day) and gave us any important information. At 9am we went to assembly (with all the other kids at the school) for about 25 minutes and then we all went our separate ways to take our individual subject classes from 9.30am. The 29 kids I was with from 8.45am to 9am weren't the same 29 I was with for the rest of the day. We didn't all take the same subjects. In some of my (subject) classes, there were only about 10 students, in others there were up to 40.
Can you see why I didn't want to start explaining this?! ;-)