First Year is a term used by current Academy students, and is equivalent to saying "Junior".
Second Year is much the same as First Year, though it is the equivalent to "Senior".
These probably arose because calling yourself a Junior or a Senior seems a bit out of place in a two-year program. (This also follows trends among colleges to use first year to describe freshmen and transfer students.)
It is also common practice at the Academy to refer to the class that most recently graduated as third years. This could probably be extended further, but rarely will current students know any of these classes. (One exception is Kyle Williams, a Pacesetter that continues to return to the Academy for no apparent reason. Most people find his presence to be unfortunate, and he is often refered to as Douchey McDoucherson.)