Class C3 at Coal Hill School was taught by Ian Chesterton in 1963; he taught science. (PROSE: Nothing at the End of the Lane) It was a fully equipped science lab, (PROSE: Nothing at the End of the Lane, Time and Relative) complete with Bunsen burners. (PROSE: Time and Relative) Among the class's students was Susan Foreman. (TV: "An Unearthly Child", PROSE: Nothing at the End of the Lane, Time and Relative)
On 26 March 1963, Ian spent the whole class teaching his students that "magnesium burns". Susan, bored with this rather obvious "revelation", had in mind to take out one of her grandfather's ever-lasting matches, and see what he'd make of that.
On 1 April, April Fools' Day, Ian sent Little Titch Critchley to fetch a "left-handed blackboard rubber" from the supplies cupboard, knowing full well there was no such thing. (PROSE: Time and Relative)