This is slightly different in British vs American English. In the UK we would say "mark" to mean the score on a test. We would only say "grade" to refer specifically to letter-grades scores on a test (A+, A, B, C etc). In the UK we most frequently use "mark/marks". I have heard Americans use both but someone else would need to verify that. Americans would also say "grade" to mean the school-year class that you are in (1st grade, 2nd grade, 3rd grade etc - each one year older). In the UK we would say "year" for this (Year 1, Year 2, Year 3 etc - each one year older). The school systems in the UK and USA are a bit different, so Grade and Year do not match exactly in number.

I think that the answer here may be culturally specific, as a British person I "personally" see mark used for a single piece of less important work (a homework perhaps) and a grade for an exam perhaps. I believe this is different than standard US usage. Another difference is that mark can be a number, maybe a 9 out of 10. But a grade is often a letter from A-F for example. Finally you can get both. For example "I got a mark of 68 - which is about a B I think"

Hi Ivan, It’s a difference in dialect: “mark” is very UK/Commonwealth English, and US English uses “grade” for the score or letter on a scale that students receive. I disagree with Jordan; I have never heard “mark” used in US English by Americans who live entirely within US culture. I can imagine more cosmopolitan Americans using the Commonwealth word to talk with non-US people because it is common outside the US. US English also uses the word “grade” for the student level in school: six-year-olds are in first grade and so on.

I am a teacher at a Sixth form college in the UK. We use "grade" when we refer to the overall, usually from A-E or 1-9 in the English school system and "mark" when we talk about the individual "units" awarded for example within the test. So a test could have 25 MARKS and if you get 90% of that you'd get a GRADE A. (if you speak Russian - sorry, assuming from your name - it's like оценка = grade and очки/баллы = marks)

These are interchangeable. However, I more often hear the word 'grade' used.