WASHINGTON – High school students at the elite Sidwell Friends School displayed swastikas during an afternoon assembly Wednesday, the head of the private academy informed families in a letter. The incident happened during an interactive portion of a presentation about a student-run nonprofit that uses soccer to build community among refugee children in the Washington region, according to the letter. The presenter had students use Kahoot, an online game that allows people to build their own quizzes, to answer questions. Students responded by using their cellphones, and their answers were projected onto large screens. The projections were quickly turned off when an administrator saw that two of the students’ usernames included swastikas.