The most common and most likely answer to this crossword clue is the 8 letter word WEEKDAYS
I've seen this crossword clue in Independent
W
E
E
K
D
A
Y
S
Buddy explains!
The straight part
We know that "when one goes to school" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when one goes to school = weekdays.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WEEKDAYS mean?
WEEKDAYS noun- A day of the week except those which form the weekend; that is:
- Any day of the week (Monday through Sunday).
- On weekdays.