Jacob Kounin was an educational psychologist and classroom management theorist. He studied classroom behavior and developed principles for managing student behavior and movement in the classroom. Some of his key principles included with-it-ness, where the teacher is aware of what all students are doing; overlapping, where the teacher attends to multiple events at once; and momentum, where lessons are kept moving with smooth transitions to maintain student engagement. Kounin's work emphasized the importance of actively involving all students, addressing misbehaviors promptly, and designing engaging lesson plans to minimize off-task behavior.