Group of friends sit outside front of school (5)
I believe the answer is:
posse
'group of friends' is the definition.
(I've seen this before)
'sit outside front of school' is the wordplay.
'sit' becomes 'pose' (as in sitting for a painter).
'outside' is an insertion indicator (some letters go outside others).
'front of' says to take the initial letters (the letter at the front of the word).
The initial letter of 'school' is 's'.
'pose' placed around 's' is 'POSSE'.
(Other definitions for posse that I've seen before include "Group of sheriff's men" , "Group formed by sheriff" , "Sheriff's team" , "Gang" , "legal team" .)