First Grade.
( First ( Grade . ) )
(ROOT (NP (NNP First) (NNP Grade) (. .)))
My brother is on first grade.
( ( My brother ) ( ( is ( on ( first grade ) ) ) . ) )
(ROOT (S (NP (PRP$ My) (NN brother)) (VP (VBZ is) (PP (IN on) (NP (JJ first) (NN grade)))) (. .)))