Class 2-A
Class 2-A is the 8th grade class that the Evangelion pilots Shinji Ikari, Asuka Langley Soryu, and Rei Ayanami belong to. Among their classmates are Hikari Horaki, the class representative, Touji Suzuhara and Kensuke Aida. The students are provided laptops to aide their studies which appear to all be networked.
In Episode 03, Touji notes that the class has thinned out, and Kensuke states that the Angel attack (specifically the battle against Sachiel) has forced people to move out of Tokyo-3 or transfer to other schools. In Episode 17, Ritsuko reveals that all of the students in Class 2-A are potential 4th level pilot candidates and in Episode 19, that information is relayed to Shinji.
According to the evacuation announcement during Shamshel's attack, it seems that the entire school consists of elementary and middle grade classes. In the Japanese school system, elementary school starts at grade 1 to grade 6 and middle school starts at grade 7 to grade 9. The first number in the class is the grade for the specific level of education (middle school in this case) and the letter denotes which of the specific classes of that grade. This designation also applies to the classroom, since the students stay in the same room throughout the school day while the teachers for a given subject switch classrooms. This is corroborated when in Episode 09, a student mentions that Asuka is in the 8th grade and in Episode 17 when the old teacher tells the class that Mr. Koike is absent so the modern Japanese class will be self study.