Don't stop asking for that handshake. It's symbolic of the attitude you as the teacher are trying to develop in those two students. It's very difficult for victims to forgive, but an angry victim may only seek revenge at a later time on his own. Bullies need to learn how to ask for forgiveness. Victims need to work on accepting it. We as teachers and as adults can be an example to our students and to our children by asking for and receiving forgiveness ourselves