Maxes out in tests (5)
I believe the answer is:
exams
'tests' is the definition.
('exam' can be a synonym of 'test')
'maxes out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'maxes' is an anagram of 'EXAMS'.
'in' acts as a link.
(Other definitions for exams that I've seen before include "Cut up writing" , "Tests for students" , "Student assessments" , "Set of exercises evaluating knowledge (abbr)" , "Important tests" .)