A non-threatening strategy to discover potential areas of misunderstanding. A box is set up as a 'post box' into which pupils 'post' questions. The teacher collects the 'post', reads the questions at random and addresses any misunderstandings in session with the whole class.

A post box (United Kingdom and others, also written postbox), or mailbox (United States, Canada and others) is a physical box used to collect outgoing mail, that is mail that is to be sent to a destination. Post box can also refer to a letter box for incoming mail.