The radio operator calls my aircraft up asking if we're ready for departure and my student replies in the affirmative
Err... no you were not ready for deeparture... you were ready for a backtrack.
Student then announces 'lining up'.... We roll out onto the runway, and backtrack about 20m.
Err....no he wasnt lining up... he was backtracking! You said so yourself!
Perhaps if more accurate RT had been used, indicating what you were actually doing, the Pitts pilot would have been more in the loop. Im sure he didnt expect a mere 20m backtrack!