The Digital Activity Center at Peace First, a Boston-based organization, provides a gamut of resources for peace education. Very teacher friendly and free! https://www2.peacefirst.org/digitalactivitycenter/resources/search
The United States Institute of Peace's glossary of terms for conflict management and peacebuilding. https://www.usip.org/sites/default/files/peaceterms.pdf
Conflict analysis - the ability to identify the root causes of a conflict - is a fundamental skill for peace-building. Nothing helps kids learn this skill more quickly than role play. Acting out someone else's conflict builds empathy as well as critical competency. Some schools in Australia have SCRAM https://www.scramwa.com/ a mediation competition that is very similar to our mock trial program. Materials for the program are free online and include lots of role plays that are relevant to teens. Try having your class role play and nonviolently resolve a conflict. You might be surprised at the insights and compassion of your students.
The Summer Institute on Kingian Nonviolence offered at the Univ. of RI Center for Nonviolence and Peace. https://web.uri.edu/nonviolencesummerinstitute/