The most common and most likely answer to this crossword clue is the 10 letter word HEADMASTER
I've seen this crossword clue in The Daily Telegraph
H
E
A
D
M
A
S
T
E
R
More clues leading to the result HEADMASTER
- Senior instructor getting post in footer? The opposite!
- Theresa May almost moved to embrace leader of department, one high up in education
- School captain‘s striking effort, blocked by post …
- Principal shared meat out
- Difficult terms ahead for someone like Squeers?
- Principal title held by Pole? Just the reverse
- School boss gives the fellow a sad term unfortunately
- He has to arrange terms ahead
- Principal trade has me befuddled
- Principal read ‘Sam’ the novel
Buddy explains!

The straight part
We know that "School captain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case school captain = headmaster.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 HEADMASTER mean?
HEADMASTER noun- A male school principal.