Group dynamics is a powerful thing, people. We are watching the same movie (Nine Queens, and if you haven’t watched it, you are wasting your life) in two sections of my Spanish Beginners II course. The course is the same, the material is the same, the classes meet on the same days and in the same building.
Yet, the group dynamics is very different. The two groups of students laugh in different places of the movie. They have a completely different collective reaction to it.
This is something that I observe all the time. I prepare an original activity, bring it to class, and the students love it. The activity works brilliantly, the students are very enthusiastic, and we achieve great progress in class. Two hours later, I bring the same activity to another section of this course. Students are bored and indifferent and the activity bombs.
A group is so much more than the individuals making it. It has a life of its own.