私は、〇〇大学附属高校に通っていましたから、大学の友達は、ほとんど知っています。
I went to 〇〇大学附属高校, so I know most of my friends in university.
It’s really rare that the freshman college students already know many students before they start college in US. But it’s not rare in Japan. There’s several famous college or university attached high school, junior high school, middle, sometime elementary. 😮
How about in your country? 🧐