Yet that is exactly what Steve Watt, the ambitious head of Hailey Hill school in Hertford, did this week. And he could not have hoped for a more uncompromising message from Chris Eubank, the former world super middleweight champion, even if some of the language may have raised eyebrows among the inspectors.
"What good is it being world champion if people think you're a wanker?" he asked, referring to his friend Mike Tyson.
"It's easy to lose your temper. Mike hasn't applied himself to control his and people don't like him."
In between reciting poems and answering questions on his career, Chris Eubank told the 50-plus pupils that he had behaved worse than them at their age - no mean feat since all boys at Hailey Hill have been excluded from mainstream schools.
He reeled off a long list of schools and secure units which he had passed through, and said that by 1981 he was making his living as a professional shoplifter.
"I'm ordinary just like you," he said, despite his penchant for monocles and canes. He also revealed that at school he was known as "Hoover" and "double-barrelled shotgun" because of his broad nose.
"Like you I had too much energy and didn't know what to do with it. I'm not proud of it. What I am proud of is that I made the choice to do something with my life and did it."
His philosophy fits neatly with that of Mr Watt, who urges his pupils to ignore the disruptive tag that society has placed on them.
Mr Watt, who took over the local authority special school last September, plans to increase the number of GCSEs on offer from five to nine next year.
He hopes that Eubank's support will help raise the pound;50,000 needed to bid for sports college status.
"He was excellent today. I've been teaching for 25 years, but he made me feel inadequate," he said.