I'm in the first year of middle school

[keannu]

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?

wr-26
ex)I'm in the first year of middle school./I'm in the sixth(seventh) grade.

[keannu]

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.