Period of teaching (6)
I believe the answer is:
lesson
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">period of teaching</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lesson that I've seen before include "Instructive experience" , "Sermon or lecture" , "A sermon or tutorial" , "Church reading" , "School period" .)