Agree it all whizzes by, but the whizzing accelerates becsuse contact with school decreases after the end of primary. Suddenly instead of all those assemblies, sports days, plays, world book days, it''s just twice a year for parents' evening.
Years 12 and 13 are NOT part of secondary education though, whether they take place in a 'secondary school', 3-18 academy or FE college.
Officially the education stage delivered in Year 11 and Year 12 (A levels, Btec etc) is part of the tertiary stage, which includes both FE (further education i.e.beyond secondary....A levels and Btec) and HE (Higher Education I.e higher than further....degrees, diplomas, certificates at university etc).
Prom is a US import and compulsory education no longer finishes at 16 so it just muddies the waters a bit. As do counties with the tripartite 'middle school system'
Yawn....sorry, I am boring myself!!