Are the following all right? What about "I'm grade seven in middle school"(Canada) or "I'm seventh grade in middle school"(US). Is all "of" interchangeable with "in" in this context?
ex)I'm in the first year of middle school./I'm in the sixth(seventh) grade.
When I was in Canada, I heard my native speaker coworker saying "I learned Taekwondo when I was grade 2", but probably I misheard what she said.