A high school or secondary school was the last stage of a requisite pre-collegiate curriculum for children usually in their early to late teens.
In 2024, Chris Brynner told Jadzia Dax that he got a Māori tattoo on his arm in high school in the 1990s, but had to remove it. (DS9: "Past Tense, Part I")
Amanda Cole and Charles Tucker III went to rivaling high schools in Florida in the 22nd century. (ENT: "Harbinger")
While Jonathan Archer was briefly stranded in the 31st century, Daniels told him that he had learned to communicate through time in high school. (ENT: "Shockwave, Part II")
In 2153, upon her correctly guessing his hometown, Kemper informed Hoshi Sato that he hadn't lived in Duluth since junior high school. (ENT: "The Xindi")
In 2154, several high schools were reportedly named in honor of Starfleet Captain Archer following the salvation of Earth against the Xindi. (ENT: "Home")
Elizabeth Dehner was aware of her high esper rating since secondary school. (TOS: "Where No Man Has Gone Before")
Among the events occurring on the day in 2367 that Data documented for Bruce Maddox in a personal log was a secondary school play. (TNG: "Data's Day")
Kathryn Janeway played on her high school's tennis team in the mid-24th century. (VOY: "Future's End")
Lieutenant Commander Geordi La Forge attended Zefram Cochrane High School in the same era, which he told a disgusted Zefram Cochrane himself in 2063. (Star Trek: First Contact)
Tom Paris had originally planned to join the Federation Naval Patrol after finishing high school, but his father had different ideas for him. (VOY: "Thirty Days")
While stranded together in 2372, Neelix and Paris fed a recently hatched reptohumanoid creature and Neelix stated that it was their responsibility to feed it because they'd disturbed it. Paris responded with the statement "and you expect to take care of this thing until what? It graduates from high school, college?" (VOY: "Parturition")
While trying to sneak past the Swarm's ships in 2373, Janeway compared it to high school saying, "when I was in high school, I snuck out of the house a couple of times late at night. I had to tiptoe past my parents' bedroom." (VOY: "The Swarm")
In 2375, Kasidy Yates asked Ryan in the Bashir 62 holoprogram if he went to high school in Asheville. (DS9: "Badda-Bing, Badda-Bang")