The London-based personal, health and social education consultant was shocked but unfazed.
"You don't say, 'You can't have those views'. You have to present them with an alternative," she said.
Last year, Ms Burnell completed the DfES's one-year certificate in PHSE.
She believes such courses are vital if teachers are to pass on accurate and relevant information.
"Yes, it's important to have the facts and figures," she said. "But it's also about knowing the needs of a group, planning effective sessions. You can't just photocopy worksheets."
The training can plug the gaps in knowledge and boost confidence, she said.
"If teachers feel comfortable delivering sex education, then young people will learn from it."
Photograph: Richard Lea-Hair