A teacher can't initially make out where pupils come from (9,4)
I believe the answer is:
catchment area
'where pupils come from' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'a teacher can't initially make out' is the wordplay.
'initially' indicates taking the first letters.
'out' indicates an anagram (out can mean wrong or inaccurate).
The first letter of 'make' is 'm'.
'a'+'teacher'+'cant'+'m'='ateachercantm'
'ateachercantm' anagrammed gives 'CATCHMENT-AREA'.
Can you help me to learn more?
(Other definitions for catchment area that I've seen before include "River drainage basin" , "Area from which rainfall flows into a river" , "Region from which a school's pupils are drawn" , "school district" , "Terrain from which a river is fed" .)