This room is a chemistry classroom that is ridiculously long, as it runs for about half the length of the balcony. It is so long it even has two doors, one at the front and one halfway along. The teacher at the front needs to shout for those at the back to hear, and even then all you can hear is a muffled 'atoms blah blah, elements, ions, isotopes, subatomic particles yadda yadda'.
Room 12 also has old wooden desks which mean you can read inscriptions from decades ago.