Founded in 1893 as Manzanita Hall, Harker has three campuses: Bucknall, Union, and Saratoga, named after the streets on which they lie.

In 1891, Stanford University founding president David Starr Jordan influenced Frank Cramer to open the Palo Alto Preparatory School for Boys.

[8] The Manzanita Hall school began at 1129 Parkinson Avenue in Palo Alto, California.

[8] in 1919, Manzanita Hall was purchased and renamed Palo Alto Military Academy, which remained until 1972.

[8] In 1917, the enrollment was 40 girls and it served as a preparatory school for competitive colleges such as Stanford University.

[citation needed] The middle school is located on the Union campus, the former site of the Harker Preschool.

[19][23] Beyond medal winners, Harker School has sent numerous students to represent the U.S. team at International Olympiads.

[52] Each year, several Harker students receive perfect scores (no wrong questions) on AP (Advanced Placement) exams.

[53][54][55][56] In 2013, 10 Harker students received perfect scores, more than 10 percent of the total worldwide that year.

[53] Harker School offers an athletics program which includes football, volleyball, soccer, track and field, basketball, baseball, tennis, golf, softball, lacrosse, cross country running, swimming, water polo, wrestling, cheerleading, yoga, fitness, physical education, and dance.

In August 2017, Harker finished construction on their new athletic center on the upper school campus.

[65] In addition, Harker began an economics magazine, Equilibrium, in 2019, and will maintain both an online presence and print its inaugural version in summer 2020.

The school's art and literature magazine (HELM), has published 17 print issues as of late 2017.