I am not a teacher, but if I may be so bold, that's how I understand the paragraph in bold print: In a large class the teacher hands out worksheets with exercises which the students have to work through on their own (or maybe together with the student sitting next to them). For this task they will be given a certain time, maybe 5 or 10 minutes. When the time is up the teacher will then discuss the solutions with the whole class. I could imagine that the teacher asks students in turn to give an answer to one of the exercises. These answers could then be discussed with the whole group before the teacher gives the correct solution.