Cricket, say, is popular when attending school (6)
I believe the answer is:
insect
'cricket say' is the definition.
(cricket is an example)
'attending school' is the wordplay.
'attending' becomes 'in' (I've seen this in other clues).
'school' becomes 'sect' (sect can mean a faction or school of thought).
'in'+'sect'='INSECT'
'is popular when' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for insect that I've seen before include "The entomologist studies this" , "Praying mantis, say" , "Creepy-crawly" , "Possibly fly" , "Invertebrate, often winged" .)