Human body-language is one of the richest and most obscure sources of information in inter-personal communication which we aim to re-introduce into the classroom’s ecosystem. In this paper we present our observations of student-to-student influence and measurements. We show parallels with previous theories and formulate a new concept for measuring the level of attention based on synchronization of student actions. We observed that the students with lower levels of attention are slower to react then focused students, a phenomenon we named “sleepers’ lag”.