Wiktionary
third grades
n. (plural of third grade English)
Usage examples of "third grades".
Sixteen detective third grades, eight second grades, and three detective sergeants.
During the second and third grades I still didn't get a chance to play baseball but I knew that somehow I was developing into a player.
Once when the girls were both in school, in the first and third grades, he came charging home in the middle of the afternoon, convinced something was wrong.
You are not yet entitled to sit in conclave with the anointed warriors of the second and third grades, nor to worship the Red God, nor even to learn his hidden name.