Doctor on the Buses

Overheard on the 188, amidst a crowd of teenagers being taken out for an outing by some very young looking teachers. This, and the fact that some of the youths are sucking their thumbs, implies the school is of the 'special' variety. 'Which is your favourite doctor, Tom Baker or David Tennant?' asks one. 'David Tennant, he's always so excited about everything' replies the teacher. Clearly unimpressed, the youth asks - 'yeah, but you don't know anything about it. What do you know about William Hartnell?'