George Bush is shown in the Oval Office sitting at the Resolute desk. Bush never used this desk, and instead used the C&O desk, a walnut desk without a front panel.
The magazine running the essay contest is called "Reading Digest" here. The actual name of the magazine is "Reader's Digest." (Possibly deliberate to avoid copyright infringement.)
United States flags are incorrectly depicted in this episode, while many other landmarks and features seen in the Simpsons' visit to Washington D.C. are more accurate. In the room where Lisa gives her speech, the flag behind Homer's head is the original design, with stars in a circle - though there are only seven stars, whereas the very first "stars-and-stripes" flag had 13 stars, to symbolize the original 13 colonies. The scene in the House of Representatives features a flag behind the rostrum with 35 stars (seven rows of five stars each). The 35-star flag was first seen in 1863 when West Virginia became the 35th state, and was retired in 1865 when Nevada joined the union as the 36th state. At the time of this episode, the flag would have had 50 stars.
When Marge is discovering all the items that the hotel provides such as a shower cap and bathrobes, the colors on her reflection off the mirror are brighter (her hair is a brighter blue, necklace is orange instead of red, skin, and dress are brighter).
Lisa defeats Maria Dominguez and Truong Van Dinh at the local level yet both compete at the finals.
A sign seen upon the family's arrival via airplane states that Dulles International Airport is in Washington, DC. Although Dulles is the primary airport used by people going into and out of Washington, DC, the airport itself is actually located in the State of Virginia.
Lisa says, "And who did I see taking a bribe but the 'Honorable' Bob Arnold?" That should be "And whom did I see."