Lab gear reassembled for school subject (7)
I believe the answer is:
algebra
'school subject' is the definition.
(branch of mathematics)
'lab gear reassembled' is the wordplay.
'reassembled' is an anagram indicator.
'lab'+'gear'='labgear'
'labgear' anagrammed gives 'ALGEBRA'.
'for' acts as a link.
(Other definitions for algebra that I've seen before include "Part of the maths syllabus" , "letters here set out the problem" , "Symbolic mathematics" , "A garble (anag) - branch of mathematics" , "'Branch of mathematics, uses letters and symbols (7)'" .)