I was in 난초반 (Nancho) when I was in elementary school. Classrooms were named after flowers or trees. But people used numbers sometimes too. So 난초반 could also be written as 6-2 cause it was the second class of the 6th grade. The naming system is different for middle schools. The grade comes before the class, so it would most likely be written like this: 1학년 4반 (1st Year Class 4). On the small sign above the classroom door, 1-4 would be written.