The school system is so completely different between the two that'd need it's own dedicated post than a casual high school=secondary school, grades=years. thing. I can maybe do it tomorrow. I think I've got it figured out quite well.
Also it means fun? I'm aware of the phrase "What's the craic" as in, "what's up". And I use eejit myselfy from time to time. It's much nicer sounding word to use than idiot. Or I'll go the occasional I.D.Ten.Tee.
Aa, Bee, see, dee, ee, eff, jee, hach, eye, jay, kay, ell, emm, enn, oo, pee. kew, arr, tee, ess, you, vee, double-you, ecks, why, and zed.
(now I know my ABCs, will you come now sing with me)