上課 的英文怎么说?

(上課到一半接起電話或傳訊息等)我正在上課 = I am in class.
其他班級還在上課 = Other students are still in class.
我等一下要上課 = I am going to class later.
我等一下要教課 = I am going to teach a class later. = I have a class to teach later today.
我下班後還要上課(進修) = I have class after work.

teach a math class = 教數學課
teach an English class = 教英文課

Q: 請問有 They are having a class. (他們正在上課) 這種說法嗎?

A: 外國人雖然聽的懂 They are having a class.，卻非自然的英文，所以不建議使用，建議使用 They are in class.。