Probably not helpful to Gromit, but on the right topic.
Many years ago, I worked in Language department of a College. Sometimes at very short notice I had to "teach" a small class of engineers who were learning basic conversation French as part of their engineering course. It was such short notice, ie about twenty minutes, that there was no time to prepare. So I just decided to only speak French in that class,( yeah revolutionary I know!) and ask them to explain to me what they had been learning the previous week. Then, according to the chapter of the book they were on, I would just make up questions on a similar theme. It seemed to work and they seemed to enjoy it.