For any rejoin ,you must be below the other aircraft,and at least a `span `out..Depending on a/c type,usual line is nose/spinner-wingtip,and no further forward than elevator/rudder ...If either you or student go `,blind`,then that is an automatic `Breakaway/Out,` and call.
Strongly suggest you get hold of an instructor and `refresh`,otherwise it `could end in tears......!