Gus Hooker wanted to support and raise money for the annual month-long charity event as his grandfather recently beat cancer, reports BBC News.
However, he was told that he was prohibited from doing so by Priory Academy in Dunstable, Bedfordshire as the fundraising event wasn't "entirely inclusive".
The school added that it was "not an activity that many children would be able to join in with".
Hooker said: "Because I can grow a moustache, I reckon that if I did it I could raise a fair bit.
"I just wanted to show off my moustache. Everyone wanted me to go for it."
The school has instead given Hooker permission to organise a 'fake moustache day'.
> 'Parks and Rec' Nick Offerman instructs how to grow Movember moustache
> Scroobius Pip vs Movember: 'No Momo' - video