yelling in my son's face?! seriously?

I'm having some issues (to put it mildly) with W's teacher. I had several 6th grade students tell me that W accidentally broke a piece off a project that a 6th grader had made (lower grades were allowed to view and test the circuit boards made by 6th graders) and when he told his teacher he didn't break it on purpose, she called him a liar, told him to stop lying to her, and continued to yell in his face. These students told me individually, all stating the exact same story of what happened. They also said they felt badly about how W had been treated. I e-mailed the principal (she told me to talk to the teacher) so I e-mailed the teacher and cc'd the principal. I am livid.