Conversation

I gave in yesterday. The day before the state exam, and after two weeks of heavy test preparation, I allowed my students to relax. I gave them a few final reminders and then allowed them to have "free" time.
The fundamental level class amazed me. They started into the horseplay, the rough-housing. I had to make them sit down. When I asked them to just have a conversation with each other, they replied, "What should we talk about?"
The other classes know how to have conversation. They could talk about sports, the news, or pop-culture without engaging in physical interactions.
I'm confused.