"Right, shall we get practising then? I was thinking, the first thing we should do is Expelliarmus, you know, the Disarming Charm. I know it's pretty basic but I've found it really useful -"
-- Harry Potter beginning the first meeting of the D.A. (OP18)
Thanks to a tip from Dobby, they find a place to meet – the Room of Requirement – and spend the first lesson working on Expelliarmus.