[2] The thirty-year-old Terrill elected to get his second bachelor's degree from Yale, and graduated in just two years as the class valedictorian.

The six original teachers included Terrill, his wife Ada (one of the first female graduate students at Yale), and his father, James, a former college president.

[7][8] Within two years of its creation, TCD was advertising that its faculty included a "Rhodes Scholar and Harvard, Dartmouth, and Amherst men.

"[citation needed] Under the leadership of board chairmen Wirt Davis (the head of Republic Bank) and Eugene McDermott (the founder of Texas Instruments), TCD heavily prioritized academics in the same manner as the early Terrill School.

[7] To bankroll his aspirations, McDermott recruited his Texas Instruments co-founder Cecil Green as another key donor.

[7] TCD headmaster Robert Iglehart headed the merged institution,[7] but representatives of both schools sat on the board of trustees.

[4] The new St. Mark's was and still is a nonsectarian institution, but the religious name reflected Cathedral's influence,[11] and the school continued to employ an Episcopal chaplain.

Headmaster Ted Whatley called St. Mark's "a Sputnik school founded by industrialists to improve science and math education in Dallas.

[citation needed] At least one alumnus, Alan Stern, traces his NASA research to his participation in the St. Mark's planetarium, observatory, and astronomy club.

[31] In contrast to the Terrill School, which was spearheaded by its founder and failed after he died, St. Mark's has been driven by donors, most of whom have actively served on its board of trustees.

[32] In addition to McDermott and Green, notable donors include the families of Harlan Crow,[33] Kenneth Hersh,[34] Lamar Hunt,[35] Tom Hicks,[36] and Elliott Roosevelt.

[37][38] The school continues to raise large amounts of money from deep-pocketed donors, completing a $112 million fundraising campaign in 2013.

[40] In 2018, Architectural Digest named St. Mark's the most beautiful private high school campus in Texas.

[17] In the 2024-25 school year, St. Mark's charged students an average tuition of $35,683,[16] ranging from $31,435 for first-graders to $39,355 for twelfth-graders.

[54] During the decade of the 1910s, Terrill began to recruit enough athletes (including boarders in a postgraduate year) to successfully compete against much larger high schools as well as teams of college freshmen from Rice, SMU, and TCU.

[58] For example, one head coach of that era, Eugene Neely, had starred in football at Dartmouth, despite having lost an arm in a hunting accident at age 14.

Another coach, Monroe Sweeney, left Terrill for Major League Baseball, where he umpired 412 games.

Another, Pete Cawthon, left Terrill to coach at Austin College, bringing with him 7 of his Terrill players;[59] Cawthon went on to become head football coach for Texas Tech and the Brooklyn Dodgers of the National Football League as well as the athletic director for the University of Alabama.

Varsity teams primarily compete with the sixteen other private schools in Texas and Oklahoma comprising the Southwest Preparatory Conference (SPC).

[61] For the 2022-23 school year, St. Mark's won the SPC Directors Cup, an overall measure of conference success.

[70] Before taking up acting professionally, Tommy Lee Jones ‘65 was an all-conference offensive lineman for Harvard's football team.

Aside from Jenkins, who interned for the San Antonio Spurs after college, all of these alumni entered sports management from the business world.

As of 2024, Harrison Ingram '21 is the starting forward for college basketball's North Carolina Tar Heels.

[84] While at St. Mark's, Ingram was evaluated to be the best basketball player in the state and was named to the 24-player McDonald's All-American team.

[85] The summer after graduating from SM, Ingram was a member of the United States team that won the 2021 FIBA Under-19 World Cup in Latvia.

[104][105][106][107][108] For the 4th consecutive year, the 2023-24 SM 4th grade class finished 1st nationally in the most competitive division of the WordMasters Challenge, a series of 3 tests taken annually by 125,000 4th graders around the country.

[120] In 2019, the middle school magazine won its 3rd consecutive Gold Crown, an award given to only 1 or 2 publications in the country.

In 2022, SM's The Focus was one of 2 specialty magazine to win the NSPA's top award, its 4th consecutive Pacemaker.

[136] In 2016, the President's Committee on the Arts and Humanities named an St. Mark's senior one of the 5 National Student Poets, selected from over 20,000 applicants.

[146] In 2024, a SM senior won the Princeton Prize in Race Relations, an award that goes to 29 high school students in the country each year.