International Masterclasses offer high school students from 55 countries around the world the chance, to be particle physicsist for one day. They are invited to a research institute and analyse LHC data. Each Masterclasses day ends with a video conference, where students present and combine their results. The video linkups are moderated by PhD students and Postdocs at CERN. IMC19 will be held from March 7 to April 16, plus few satellite events. The meeting will introduce moderators to their tasks. More infos about International Masterclasses: www.physicsmasterclasses.org