QuarkNet is a U.S. program for professional development of high school teachers. In QuarkNet, teachers deepen their understanding of physics, pedagogy, and how to engage students through the use of authentic data from a diverse set of contemporary particle physics experiments. The LHC figures prominently in these efforts. QuarkNet promotes and manages International Particle Physics Masterclasses with Fermilab-moderated videoconferences, has partnered with physicists to develop and maintain the CMS masterclass used worldwide, and has created new masterclass opportunities such as World Wide Data Day. QuarkNet makes these masterclasses available not only in the U.S. but also throughout the world. These international collaborations enrich the teachers and students involved. QuarkNet teachers also participate in LHC Data Workshops and similar opportunities. QuarkNet staff and select teachers are currently building short masterclasses and workshops for the 10th anniversary of the discovery of the Higgs.