I don’t know why I never knew about the Cornell Math Explorers Club before now. Its website is a terrific enrichment resource for high-school math students and their teachers, with a wonderful assortment of slightly offbeat topics that are right up my alley for all the programs in which I teach: Weston High School, Crimson Summer Academy, and Saturday Course. Their modules include cryptography, graph theory, probability, set theory, topology, game theory, and the mathematics of voting and elections. I wish I had known about this site earlier. Check it out!