Elementary school grade
(Other definitions for first that I've seen before include "higher than the others" , "Leading" , "Most important" , "Initial" , "Pre-eminent" .)
(Other definitions for third that I've seen before include "Eroica, Beethoven's - symphony" , "Next after second" , "Ruthless interrogation" , "Last of three" , "Last place on the podium?" .)