at weekend, on the weekend的分別

sandy：
其實近十多二十年年來, 英文受美文的衝擊甚大, 英文一向是用 on the weekend, 美文就用at the weekend. 究其實是同一意義如牛津字典的例句便有說明 The office is closed on the weekend------英文
The office is closed at the weekend-------美文

at weekends
at the weekend = on the weekend= over the weekend
at the weekend ----> British usage
on the weekend ----> American usage

At weekeend that means in that weekend
On the weekend that means in the top of the weekend

it depends on what kind of sentence you want to put the phrases in
for example.

"I'm planning to host a party at (this) weekend"
i added "this" to make it clear when I wanted to have the party

"I always have lots of homework piled up on the weekends"

Both phrases works the same way, it really depends what's your tone in saying the sentence you want. There's no BIG difference at all