A school bringing in second uniform in a particular capacity (2,4)
I believe the answer is:
as such
'in a particular capacity' is the definition.
(I've seen this before)
'a school bringing in second uniform' is the wordplay.
'school' becomes 'sch' (abbreviation).
'bringing in' is an insertion indicator.
'second' becomes 's' (common abbreviation).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
's'+'u'='su'
'sch' enclosing 'su' is 'ssuch'.
'a'+'ssuch'='AS SUCH'
(Other definitions for as such that I've seen before include "in the manner described" , "Intrinsically" , "in a particular capacity" , "in that particular role" .)