Question

What can we do to ensure that students do not run out of school during school classes.

Answer 1

You  can   appoint  a  student  leader  in  charge  of  this  responsibility.Tell  him  to  report  you  if  a  student  runs  out  of  school  during  school   classes. 

Answer 2

You can keep counting the children. Or you can keep a strict penalty for that children so that they may not dare to do that.