我妹妹在这所中学上学。

Wǒ mèimei zài zhè suǒ zhōngxué shàngxué.

My younger sister studies at this middle school.

我妹妹今年刚上中学。

Wǒ mèimei jīnnián gāng shàng zhōngxué.

My younger sister just started middle school this year.

他在中学的时候就很喜欢学汉语。

Tā zài zhōngxué de shíhou jiù hěn xǐhuān xué Hànyǔ.

He already liked studying Chinese when he was in middle school.