Question

Please explain why this is so:
On est rentrés tres tard hier soir.

Answer 1

On is plural so why don't we say on sont ???

Answer 2

"On"means "we", but is grammatically singular, so the verb must be singular.

Actually, I would write :
On est rentré très tard hier soir. (no "s" at the end of rentré)

Answer 3

my teacher is french she said rentrés is correct
actually i agree with you if i use est, i should use verb without s that is why im confused

Answer 4

You are right, my grammar says so too.
"On est rentrés..." is the correct form.