If American school system has the same system as Australian one, I assume each student belongs to a pastoral class or a pastoral care group at school. 〇年〇組 is an equivalent to those groups in Japan. I assume the number "216", which you mentioned above is an actual class room number, instead of the group number. 〇年 stands for a school year. e.g. ２年 means Year 2. 〇組 stands for a group number. e.g. １組 means the first group of the year and ２組 is the second group etc.
The common names for the pastoral classes are numbers, like１組、２組 and alphabets, like Ａ組、Ｂ組. However, there are other variations for rather small primary schools like 東(east)組、西(west)組, 赤(red)組、白(white)組 etc.
Thus, 二年A組 means that the first group of Year 2.