He is the fearsome broadcaster who regularly has our political leaders for breakfast. But has John Humphrys ever had a tougher audience than this?
The veteran interviewer this week ventured into an east London comprehensive to give a group of inner-city teenagers a lesson in the use, and misuse, of the English language.
The star of Radio 4's Today programme travelled to Eastlea school, a successful secondary in Newham, to film a documentary for Teachers' TV, the new Government channel which will be launched next month.
It also gave him a chance to discuss his new book, Lost for words: the mangling and manipulation of the English language.
The purpose, though, was not to drill the youngsters on avoiding split infinitives or the dangers of mixed metaphors. In fact the inquisitor-in-chief was on unusually gentle form when he spoke to The TES.
The 61-year-old confessed that he had never taken a lesson before. "This is daunting for me," he said. "I'm used to lecturing, rather than teaching."
He added that the purpose was not to tell youngsters how to talk. Young people had always adapted language, he said. In his own youth in south Wales, he and his classmated had spoken "pig Latin" - a garbled form of English with the start and endings of words exchanged.
Mr Humphrys said: "The point of my book is not that everybody should speak the same; God forbid. But we should practise the common language, the language that we use in the common space. That's the message that I hope to be able to impart."
He also said he would like to find out from the youngsters more about why most young people now swear so much, a subject he has spoken out about in the past.
Mr Humphrys was filling in for award-winning English teacher Philip Beadle as part of a series on the government-funded channel which starts in March.
Other celebrities, including actor Michelle Collins, will also take part.