In June 1953, the school moved to its present location at 119 East Craig Place in San Antonio's renowned Monte Vista Historical District.

By 1954, Edwin Eargle had added an Upper School to serve students in the ninth through twelfth grades.

The school has undergone considerable expansion over the past half century, particularly in the last fifteen years.

Whether the student wants to study full-time or just needs individual classes, they offer more than 170 courses from credit recovery to world languages.

Keystone's start of the 20th century Victorian and classical-revival campus occupies nearly a full city block of restored mansions and carriage houses between McCullough, North Main, and Woodlawn Avenues.

The following buildings and facilities can be found on the campus: Admission to Keystone is selective and limited, and is particularly competitive for prospective students rising into pre-kindergarten and the first and ninth grades.

The test, which was developed by the third-party Education Records Bureau, lasts approximately three hours and is offered on a variety of dates.

In addition, the Heads of the Middle and Upper Schools personally review the recent test scores and grades of the applicants.

Students in the Upper School must take no fewer than 21 academic courses in order to attain eligibility for the faculty's recommendation that the Headmaster confer a Diploma.

Students begin their foreign language studies in the Lower School years, taking classes in Spanish.

Keystone participates at the Alamo Regional Science and Engineering Fair and has even sent hundreds of representatives on to international competitions despite its very small enrollment.

In 2005, Keystone student Neela Thangada was named America's Top Young Scientist by the Discovery Channel and in 2006, senior Elizabeth Monier won sixth place individually in the Siemens Westinghouse competition.

[9] Class of 2018 student Nia Clements attended the International Science & Engineering Fair and White House Science Fair for her work to find a cure for gastric cancer, earning her attention from Bill Nye, Joe Biden, and Adam Savage as well as a cover for Smore magazine.

As a component of its science education, Keystone offers its students a number of field trip options at many of the grade levels.

Here they stay in log cabins in a reservation The seventh grade goes to the Outdoor School in Marble Falls.

Though not in the same conference for varsity sports, the school's traditional athletic rival is Saint Mary's Hall, which was once located immediately adjacent to Keystone, on the campus now occupied by the San Antonio Academy.

In early Autumn, from September through October, the Middle School Cross Country team competes.

Keystone's theater arts program includes acting, public speaking, dance, and improvisation as well as behind-the-scenes activities such as set design, stage lighting, and audio mixing.