The High School National Championship Tournament (HSNCT) is a premier national tournament run by NAQT every May, typically over Memorial Day weekend. The tournament is a two-day affair, with preliminary rounds Saturday and playoff rounds Sunday; there are also optional practice rounds on the Friday before.
The HSNCT currently draws the largest field of any national tournament. In 2011 it attracted 224 high school teams from 179 different schools. The most common way to qualify for the HSNCT is to finish in the top 15% at a tournament using NAQT questions during the season, though there are alternative ways listed on the NAQT HSNCT website.
The HSNCT tournament set contains 27 packets, each of 24 tossups and 24 bonuses (until 2011, it used 26 packets of 26/26). Its distribution can be found here. Matches use nine-minute halves, so it is common for a match to not get through all of the tossups in a packet. When the timer goes off, moderators finish the question they are reading, and if that question is a tossup that gets answered they read the associated bonus.
On Saturday, the first day of competition, each team plays ten matches. There are sixteen rounds, so each team gets six byes. HSNCT uses power-matching; each team is guaranteed to play each of its matches against opponents that have a record within one win of its own record. (In other words, if your current record is 3-5, then your next opponent will be 4-4, 3-5, or 2-6.) Teams need to win at least six of their ten matches to continue play on Sunday. (NOTE: This paragraph and the next one describe the format starting around 2008 and continuing through 2011. Past years were similar but not identical, and formats in future years may change based on decisions to be made by NAQT.)
On Sunday, teams that won six matches on Saturday are eliminated by their first Sunday loss, and teams that won seven or more matches on Saturday are eliminated by their second Sunday loss. With a few exceptions, teams on the verge of elimination play each other, while teams that still have one match to lose also play each other. Play continues until all teams but one are eliminated, and the rest of the final standings in the tournament are based on which teams last the longest on Sunday before being eliminated.
HSNCT also has a Small School Division, which is for schools that have 500 or fewer students in grades 10-12 and non-selective admissions. These schools play as part of the regular tournament Saturday and Sunday, but after they are eliminated from the regular tournament, they play in a separate set of small school playoff rounds to determine a Small School Champion.