A science fair was an event at which participants showcased scientific research that they performed in a chosen area of study. The displayed research would then be judged with prizes awarded to those deemed winners. Such events were normally intended for children to display work that they performed as part of a school assignment.
In 2368, the three winners of the primary school science fair aboard the USS Enterprise-D were treated to a tour of the ship personally conducted by Captain Jean-Luc Picard. (TNG: "Disaster")
In 2370, the daughter of Ensign Kelly worked with a Bajoran girl on a prize-winning science fair project. Benjamin Sisko cited this as a tie Deep Space 9 personnel had with the Bajorans which was threatened by the evacuation of Starfleet personnel due to the activities of the Alliance for Global Unity. (DS9: "The Siege")
In 2373, Odo asserted that Doctor Mora Pol would be nothing if it weren't for him, saying, "Starfleet wouldn't hire you to judge a science fair." (DS9: "The Begotten")
The USS Voyager held an annual science fair, beginning in 2376, for the children aboard the ship. (VOY: "Child's Play")