Anxious fifth grader is after perfect scores (5)
I believe the answer is:
tense
'anxious' is the definition.
(I've seen this before)
'fifth grader is after perfect scores' is the wordplay.
'fifth grader' becomes 'e' (5th letter of 'grader').
'is after' means one lot of letters go next to another.
'perfect scores' becomes 'tens' (I've seen this in another clue).
'e' after 'tens' is 'TENSE'.
(Other definitions for tense that I've seen before include "Future, possibly" , "contract" , "Stressful" , "in the past, perhaps" , "Under emotional strain" .)