An expression used to ask someone's school grade (e.g., what grade are you in). Usually used as '何年生ですか？'.
先生に『あなたは何年生ですか？』と聞かれた。
The teacher asked, "What grade are you in?"
入学式で『何年生ですか』と名札に書いてくださいと言われた。
At the entrance ceremony we were told to write our grade on our name tags as '何年生'.
いとこは小学校三年生で、学校で何年生かすぐに教えてくれた。
My cousin is in third grade of elementary school and quickly told me what grade she is in.