Of course you only had a thousand students through all those six grades.
( ( Of course ) ( you ( only ( ( had ( ( a ( thousand students ) ) ( through ( all ( those ( six grades ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN Of) (NP (NN course))) (NP (PRP you)) (ADVP (RB only)) (VP (VBD had) (NP (NP (DT a) (CD thousand) (NNS students)) (PP (IN through) (NP (PDT all) (DT those) (CD six) (NNS grades))))) (. .)))
Each class size varied.
( ( Each ( class size ) ) ( varied . ) )
(ROOT (S (NP (DT Each) (NN class) (NN size)) (VP (VBD varied)) (. .)))