So we have Chinese(sister school?)lessons.

所以我们有汉语课。（姐妹学校？）

youdao

When Catherine Hill’s mother became pregnant while a student at Harvard’s sister school, Radcliffe College, she was discreetly but strongly urged to drop out.

凯瑟琳 希尔的母亲在哈佛大学的姊妹学校拉德克利夫学院就读期间怀孕，学校得知后，慎重的要求其退学。

youdao

I was at school with her sister.

我和她妹妹过去在一个学校读书。

《牛津词典》

Her sister became a sculptor. After finishing high school at the age of eighteen, Diane married Allan Arbus.

VOA: special.2009.08.09

My sister's still in high school, so she'll be, she'll be here, too.

我妹妹还在上高中，所以她也会来这里。

身为大学生很快乐 - SpeakingMax英语口语达人

Her sister and brother were already in school when she was born.

VOA: special.2010.03.14

United Learning chief executive Jon Coles said the academy and its sister school had "great potential".

BBC: Richard Rose Academy: United Learning takes over school

We could have played ... what's Notre Dame's sister school?

WSJ: Marquette lose to Notre Dame in Big East quarters

What began as an odd hobby has grown into a full-fledged business: the school trains 4, 000 guests to hunt with hawks each year, and the Fords have opened a sister school at the Equinox, in Vermont.

WSJ: Learn Ancient Sports Around the World