Big Brother host Davina McCall surprised pupils at Parmiter's School, when she burst into their lesson.
Davina chatted to students before announcing that, as recognition for the record amounts of money the school has raised for Comic Relief, 12 pupils and teachers Katherine Bliss and Christelle
Grenham would be treated to a tour of the Harry Potter set at Leavesden Studios.
The group will also watch some filming and meet stars Daniel Radcliffe (Harry Potter), Emma Watson (Hermione Granger) and Rupert Grint (Ron Weasley).
Footage of the visit, held last Wednesday at the school in High Elms Lane, will be shown during the Comic Relief programme on BBC1 on Friday evening.