在上课

• in session
• at school
• at achool

例句

1. 他因在上课时吸烟而被开除了。
   He was expelled for smoking in class.
2. 大多数的学生在上课中没有用心。
   Most students were not attending in class.
3. 在上课期间内不要离开学校。
   Don't leave the school precincts during school hours.