Translation:I'm a fifth-grade student.
Don't know wtf they are doing behind the bird... A hyphen difference makes it a "wrong sentence"? Then what about all those fullstops and question mark often missing???
"Year five" should be accepted.
I'll just report that . . . for the fifteenth time!
I'm not sure any 5th grader would actually say "I"m in the 5th grade," at least not in America. "I'm a 5th grader" or "I"m in 5th grade" are the most likely phrases to be used.
As a native speaker of American English, I disagree. "I'm in the 5th grade" is a perfectly normal statement. In fact, I think I personally would be more likely to include the "the" in this sentence than to omit it.