Church students holding second count (6)
I believe the answer is:
census
'count' is the definition.
(censusing is a kind of counting)
'church students holding second' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England).
'students' becomes 'nus' (I've seen this in other clues).
'holding' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
'nus' placed around 's' is 'nsus'.
'ce'+'nsus'='CENSUS'
(Other definitions for census that I've seen before include "Official body count?" , "Official survey" , "Head-count" , "People count" , "Periodic count as of population" .)