I think it has an effect. When a class is too crowded in a closed room, it will affect their focus. Good classroom management must be in accordance with existing standards, when teachers teach too many students in one room, it will also be difficult to supervise. Students who sit at the back will be "left behind" from the teacher's supervision and focus on themselves. That happened according to my experience when teaching. maybe every student in a place/country will have different results.