I promised to describe accelerated pairings. This is not like March Madness, which is a single-elimination tournament featuring -only- 64 teams. Every one of the 138 teams here will play every one of the seven rounds. That's because chess doesn't take up much space, and you can have 69 simultaneous matches featuring over 1,000 contestants in one big room. (Also, chess is not much of a spectator sport, though I personally love it, so you don't need any bleachers at all).
But that is not the only difference. Chess is not much fun when a lot of matches are shut-outs, and chess teams span a great range of strengths, so organizers have come up with a way to get teams to play other teams close to their own strength.
Accelerated pairings match top-seeded teams against one another and lower-seeded teams against one another at first. And, in fact, they don't match the highest vs. lowest - the top 32 teams play the second 32 teams this way: 1-33, 2-34, 3-35, 4-36... But later on, teams play other teams that have the same number of wins and losses. At some point, they have to stop the accelerated parings, so that strong teams from the bottom 64 seeds get a chance to play up. If there were 128 teams (2x2x2x2x2x2x2), this plan to split them in halves would work the same for everyone. But there are 138 teams, so it doesn't always split evenly.
So -- top seeds like Whitney Young and Northside sometimes get stuck playing really high-seeded teams (14 and 27 last round), while 3rd seed (Evanston) gets to play a 70th seed that beat a couple of really low-seeded teams in the first two rounds.