Pupil and Student

[Sokheang Thea]

What is the difference between these words? Can they be used interchangeably?

[Tdol]

Pupil- someone studying in school.
You will sometimes hear people call those studying in schools 'students', but this is rare when talking about primary school.  However, you won't hear the word 'pupil' used for university students. 

[Sokheang Thea]

How about high school? People usually use 'students' for this level of education here in Cambodia. But when i check the dictionary students refers to ones studying at universities.

[Tdol]

With high school, you'll hear both being used.