Pull a name from the Mystery Hero jar. Don't say their name, but let kids know you are watching your Mystery Hero. If the Mystery Hero does a good job reward them, and if they aren't on their best behavior just say to the class that the Mystery Hero needs to try harder. Don't call the student out or let students know who it was.
from Faculty Focus | Higher Ed Teaching & Learning
Classroom Discussion: Professors Share Favorite Strategies for Engaging Students
"I’ll pass out two or three poker chips to every student. As we begin the discussion I ask each student to give me back a chip each time they answer a question. Rapidly the talking students use up their chips. Since they can no longer speak in the class it leaves the non-talking students to answer the remaining questions."