留学上课时，可以使用以下句子来进行日常交流：

开始上课

Let's start class. It's time for class. Class begins!

问候

Hello, boys and girls / children. Good morning / afternoon, boys and girls / teacher / everyone. How are you today？

请求学生起立或坐下

Stand up, please. Sit down, please.

询问出勤情况

Who is on duty today？ Who's helping this morning / today？ Is everyone / everybody here / present？ Is anyone away？

这些句子可以帮助你在留学上课时更好地进行沟通和互动。