Class C3 at Coal Hill School was taught by Ian Chesterton in 1963; he taught science, (PROSE: Nothing at the End of the Lane) and as such the words "Science Laboratory" were written on the door. (PROSE: Doctor Who and an Unearthly Child)
It was a fully equipped chemistry lab, (PROSE: Nothing at the End of the Lane, Time and Relative, AUDIO: An Unearthly Woman) complete with Bunsen burners, (PROSE: Time and Relative) petri dishes, test tubes, microscopes, (PROSE: Doctor Who and an Unearthly Child) and other such delicate equipment. (AUDIO: An Unearthly Woman)
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)
On 22 November 1963, (PROSE: Who Killed Kennedy) Barbara Wright met Ian in the classroom to discuss Susan Foreman. Later that day, the pair inadvertently became Susan's travelling companions aboard the Doctor's TARDIS. (TV: An Unearthly Child)