All students in first grade of senior high school in Indonesia have to pass the step called placement class. It divide into Science, Social or Literature class. In traditional method, the placement class process conducted by teachers. But, it needed much time to decide the right class for students. The proposed is using the Knowledge Discovery and Data Mining (KDD). Which is the placement class process using the classification method. In the first experiment classified instances 84.2%. The second experiment use the same data and attributes, give the best percentage of accuracy as 92,1%. The best result are using Naive Bayes and SMO. Hope in the future, it can be the solution to help teacher decide the placement class.