Enlist Teachers as Allies
Assuming you trust your child's teacher, bring her into your story. Tell her what is happening as you might tell a friend: "Joey has come home several times now and told me that Andy is following him the whole way home and calling him names." Then explain the impact: "This is causing Joey to come home very upset. He is depressed and is reluctant to go to school each morning." This way, you're soliciting the teacher's empathies and, most importantly, asking for his or her ideas in identifying a solution.