Wiktionary
twelfth grades
n. (plural of twelfth grade English)
Usage examples of "twelfth grades".
A number of us, ninth, tenth, eleventh and twelfth grades, had hardly slept sincewe'i learned of John Reddy's flight, we refused to eat actual meals our families, we refused to shower or wash or apply deodorant, brush our hair or our teeth for days and when at last word came of John Reddy's capture girls fainted dead away including certain distraught girls of the Circle whose ashy faces, sleep-deprived dilated eyes and bloodless lips had a strong impression on those of us who adored them.
Hell, Clayton was sixty-four, and he'd had her as a teacher in eleventh and twelfth grades.