To my mind the correct written way to show a date on a poster or even in a piece of writing is 11th April 2013

But my daughter is having a disagreement with her co-workers on film posters they are putting up. They insist on writing it:

11th of April 2013.

Surely the of is never written - it's merely sort of swallowed in speech. It's not like say 7 o'clock where the o' is shown?

Any views?

I'd agree, I don't think you ever write the "of" - though I might be tempted to in dialogue, which more closely reproduces what people actually say. But I think I still wouldn't.

Of? Of??? No. Just, no. Ask them if they've ever seen a poster with the date written thus. I think they'll find they haven't, don't you?

I was taught that, but I didn't believe them then and fear I'm giving into peer pressure now.

Thank you Emma, Jem, Gaius. I also picked up several official leaflets at the theatre this evening - hoping all this is enough to convince her colleagues as their in-house posters are looking a little weird.

<Added>

And job done, thanks.