Lined up the kids at the board along a big number line. Everybody picked a number : their "x." I said, "Shawn's x is at 2. However far away you are from Shawn, move that many floor tiles into the room, perpendicular to the board." They move into a lovely approximation of the graph of f(x) = |x - 2|. "Hey what kind of a shape are you guys making?" "A PARABOLA!" Practically in unison. FACEPALM.