Translation:I am an elementary school student.
When I see Japanese sentences like this, I picture a class of young kids on a field trip and their teacher approaching the gaijin to engage in conversation. You ask them questions in less than perfect Japanese, they ask you similar questions in less than perfect English, and before you know it, they want a picture of themselves with you in it. In spite of the language barrier, the foreigner and the elementary/grade/primary school children have communicated.
Certainly. Depending on context, it could be any pronoun.
"(I/you/he/she/they/we/it) (is/are) student(s)."
For obvious reasons, Duolingo doesn't make you write it out like that in your response. It is usually pretty obvious which one is correct when you are actually having a conversation.