Looking on the internet deeply has found these results:

Work in the school is the most popular phrase on the web.

Work at the school 15,060,000 results on the web	Work in the school 19,660,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Nice work at the school my friend. They had to recruit teachers who wanted to teach inside a prison, they had to establish strict separation between the people who work at the school and the prison authorities, and most dauntingly of all, they needed to invent a new curriculum because you know what? And since chef Nicolas is your teacher and I work at the school, I'd appreciate it if we kept this just between us three. I look after the big house, muck and feed 'em when she's not around and I work at the school in town and I also... I volunteer at the church sometimes... He doesn't work at the school here or anything. Didn't you do, like, some volunteer work at the school?	~ They'll fit it with a burglar alarm that will go off every time you fall asleep or when your child's doing some important solo work in the school production woo!" woo Scooter works in the school cafeteria. Finally you got this post started work in the school. I work in the school's basement where they store all kinds of weird stuff "Woo He doesn't work in the school.

Work at the school

15,060,000 results on the web

Work in the school

19,660,000 results on the web

More popular!

Nice work at the school my friend.
They had to recruit teachers who wanted to teach inside a prison, they had to establish strict separation between the people who work at the school and the prison authorities, and most dauntingly of all, they needed to invent a new curriculum because you know what?
And since chef Nicolas is your teacher and I work at the school, I'd appreciate it if we kept this just between us three.
I look after the big house, muck and feed 'em when she's not around and I work at the school in town and I also... I volunteer at the church sometimes...
He doesn't work at the school here or anything.
Didn't you do, like, some volunteer work at the school?

~ They'll fit it with a burglar alarm that will go off every time you fall asleep or when your child's doing some important solo work in the school production
woo!"
woo
Scooter works in the school cafeteria.
Finally you got this post started work in the school.
I work in the school's basement where they store all kinds of weird stuff
"Woo
He doesn't work in the school.