The St. Andrew's instrumental music program grows every year. Both the school's orchestra and jazz program have fully developed courses of study for students of different levels of experience.

The St. Andrew's Orchestra is comprised of 65 students and augmented by faculty members who play instruments. The orchestra gives four performances each year in its beautiful home, Engelhard Hall, beginning with a performance in October for Parents Weekend. After the December Christmas concert, the orchestra performs a special Winter Concert featuring a student soloist in its annual concerto competition. The year builds toward the exciting conclusion in May for the Arts Weekend performance.

Advanced members of the orchestra may also participate in the Chamber Music program, which is coached by members of the department. The students in this course perform at least four times per year in the monthly student recitals, which also include solo performances following auditions.

The St. Andrew's Jazz Ensemble is the school's big band, which performs three times per year. Students who wish to deepen their skills in improvisation take the Jazz Improvisation course, which is devoted to the study of jazz by performing in small combos that are featured in the jazz ensemble programs.

The St. Andrew's Pipes and Drums is an ensemble enabling the student to learn and perform the bagpipes or learn field drumming. The group performs outside for major events such as commencement and important athletic events as well as for Arts Weekend and Parents Weekend.

Nearly one third of the students at St. Andrew's are enrolled in private instrumental lessons. Besides a talented full time music faculty, accomplished musicians from the Mid-Atlantic region come to St. Andrew's to teach private lessons in all orchestra and jazz instruments plus guitar, piano, harp, and voice.

In addition to the busy schedule of student performances, numerous guest artists visit St. Andrew's each year to perform and to give masterclasses. Past visiting performers have included Duo Fresco (Brett Deubner, viola, and Christopher Kenniff, guitar) and Duo Terlano (Hannes Dietrich, violin, and Marie Cadieux, cello) as well as such pop and jazz performers as Vanessa Carlton and the Westchester faculty jazz quartet. The Haroldson Masterclass performance each year features an important string ensemble in a special program.

St. Andrew's is home to the annual Delaware Solo & Ensemble Festival, held in March.