Need help about telling the time

[Sumade]

Hello,
I want to ask you if it's ok to say: A quarter to 10 (just an example). The teachers of my children say that this would be wrong. We should say: Quarter to 10.

Thanks a lot

[Beeesneees]

Informally, many native speakers would say "it's a quarter to ten." Formally, your children's teachers are correct.
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Cheers m' dears!

[Sumade]

Thank you for your answer.
And cheers :)