the beach

Last week I had a discussion with one of my students.
In an english test she wrote "on the beach" I insisted that it has to be "at the beach".

When trying several dictionaries on the internet I found that both phrases are in use.

So which one is correct ?
Are both correct, but with different meanings or usage ?

both of them r correct

i cant explain this ,but i I could give an example mayebe u cant see the difference between 2 phrases

People often suntan on the beach.(no water ,just somewhere near the sea)

 He went swimming at the beach and end up with drowning.(in the water but it's shallow)

cool…. thanks for the idea.

Thank you.

So, it´s "at the beach", when being there to swim or being close to the water and "on the beach" when being just at the coast where the sea is near.

This makes sense.

Thanks a lot.

btw…
I also asked an American friend of mine, he didn´t know either :-)

Between the eyes of love I call your name
Behind the guarded walls I used to go
Upon a summer wind theres a certain melody
Takes me back to the place that I know
Down on the beach

The secrets of the summer I will keep
The sands of time will blow a mystery
No-one but you and i
Underneath that moonlit sky
Take me back to the place that I know
On the beach

Forever in my dreams my heart will be
Hanging on to this sweet memory
A day of strange desire
And a night that burned like fire
Take me back to the place that I know
On the beach

It is a song by an English singer Chris Rea

You have to put a full sentence in order to get the right answer. 

1. Where were you today? We were at the beach.

 2. Where did you build the bonfire last night? We built it on the beach.  

 3. I love a day at the beach. 

At the fair, at the beach, at the hospital, these all have similar meanings but there are variations, too. I suspect that 'at the beach' is the meaning you meant but I would have to see the full sentence to answer you.