What's the difference between 'mark' and 'grade', in an educational context?

In common American English usage, I think the two are synonyms. "My mark was a B+", "My grade was an 89" ... I don't think anyone would find those statements puzzling.

In American English, 'mark' is not commonly used to describe anything along these lines. At least, not in the West, Mid-west, or Alaska, where I have been. If someone said, "I got good marks in class," most everyone I know would either not understand the sentence or have to think about it for a moment. This may not hold true for New England, California, or other areas where I have no experience and the word may be more commonly used.

To better answer the question directly, if spoken in areas of the USA I have been in, the two would be seen as synonyms. The listener may assume the speaker is British, and that assumption may carry other connotations with it, but the words themselves would not be used differently nor carry different connotations.

In British usage, a marking scheme is usually drawn up for an exam or test. The completed papers are marked (the mark being a number, out of perhaps 100 marks available). Ignoring moderation (where the test itself is judged and grades and possibly even marks are adjusted), perhaps the top 10% of candidates are awarded an A grade, the next 20% a B, the next 30% a C, the next 20% a D, and the rest an E or an F.

Marks is used commonly in Canada. Marks is actually used more than "grade" or "score". It's common to hear kids ask, "What mark did you get?"

Mark means more like to literally mark right/wrong answers, but does not necessarily imply that a grade is given. Grade means to give an actual grade, which may or may not involve marking beforehand. Hope this helps!

I found this explanation:

More specifically, a mark is the level of achievement against specified criteria for an assessment item (e.g. a mark of 30/40 for an assessment). A grade is the overall level of achievement for a course, usually determined by combining the marks of the individual assessment items that make up the course.

source: What is the difference between a mark and a grade?

(I am not a native, learned and studied British English at school, but never studied in an English speaking country.)