Eastside Prep was founded in May 2002 by a group of parents and educators seeking more school choice, with a focus on interdisciplinary work and strategic thinking. Dr. Terry Macaluso, previously Head of School at Lakeside School, was a consultant to the founders and subsequently became the Head of School at Eastside Prep. The school opened its doors in September 2003 with 16 students in grades 6 and 7, along with 3 full-time and 1 part-time faculty. Eastside Prep graduated its first class of students in 2009. Eastside Prep has expanded each year, adding students, faculty, administrators and buildings. At the beginning of the 2018-19 school year, the school has over 100 employees and over 480 students in grades 5–12. In fall of 2015, Eastside Prep expanded, completing the construction of a new 4 story building that includes a gym, science labs, a design lab, an amphitheater and several multi-purpose classrooms. In fall of 2018 the school's newest building opened. TALI is a 50,000 square foot building housing a 500+-seat theatre, new art studios, a set shop, instrumental and choral music rooms, science labs, general purpose classrooms and administrative offices.
Eastside Preparatory School has multiple robotics teams, in two separate leagues: FIRST Lego League for middle school students, and FIRST Tech Challenge for students in 7th grade or higher. They have three FTC teams, a varsity team named Void Robotics, a varsity team named Null Robotics, and a junior varsity team named Undefined Robotics. Null Robotics has won multiple awards. During the 2017-2018 season they most notably won the PTC Design Award. They won Tesla Interleauges in 2018. All three teams design and machine their own parts through innovative methods such as 3D Printing and CNC Machining.
Athletics
In addition to Physical Education courses, Eastside Prep offers a number of afternoon sports. Eastside Preparatory School has a gym as of 2015. In 2012 the Eastside Prep Eagles opted up to the Emerald City League 1A athletic conference competing against much larger prep schools. In their league are The Bush School, The Overlake School, Seattle Academy of Arts and Sciences, University Prep, Northwest School, the Annie Wright School and the Forest Ridge School of the Sacred Heart. Fall sports offered include Coed Crew, MS Boys Soccer, MS Girls Soccer, MS Coed Cross Country, MS Girls Volleyball, US Girls Volleball, US Boys Ultimate Frisbee. Winter sports offered include 5th Grade Coed Basketball, MS Boys Basketball, MS Girls Basketball, US Boys Basketball, US Girls Basketball, Seasonal Ski Bus. Spring sports include Coed Crew, MS Co-Ed Track and Field, MS Coed Ultimate Frisbee, MS Coed Tennis, US Co-Ed Track and Field, US Girls Ultimate Frisbee, US Boys Soccer.