Delphian School is a private, co-educational K–12 boarding and day school near Sheridan, Oregon, operated by Delphi Schools on a 720-acre campus. Founded in 1976, Delphian primarily serves students in grades 8–12, with most living on campus either full or part-time. It uses study techniques created by Scientology founder L. Ron Hubbard, known as Study Tech. Day students and boarders must meet specific age requirements. Accredited by Cognia and the Northwest Association of Independent Schools, Delphian curriculum is self-paced without traditional grades or grade levels.

In the fall of 1976, Delphian School opened on the site of a former Jesuit novitiate near Sheridan, Oregon. The main building on campus is a four-story, Art Deco-style building with a brick exterior designed by Poole & McGonigle and built in 1933 for the Jesuit house.

In 1974, the order sold the building and surrounding acreage to Delphian. The former novitiate was then converted to a boarding school, as it already featured dorm rooms, classrooms, and a dining hall with a commercial kitchen.

Opening in 1976, Delphian School created a curriculum for grades K-12. There were about 60 students in the school's first year. Two years later in 1978 the school had 120 students; tuition was $4,500 for boarding students and $2,800 for non-boarders. In the mid-1980s the campus was considered as a possible location for a federal prison. The Sheridan Federal Correctional Institution opened in 1989 in another location in the area.

The headquarters for Delphi Schools, Inc. are located at Delphian School, which is the founding school.

During school closures due to COVID-19, Delphian School offered free online classes.

Delphian School uses Study Tech—techniques invented by Scientology-founder L. Ron Hubbard and licensed through Applied Scholastics. This includes students progressing based on completion of steps in the curriculum and not of the traditional letter grades, report cards, and grade levels. Students advance through the curriculum at their own pace rather than in a set time with a class.

The school is the location of Heron Books, which published textbooks and materials using Hubbard's educational techniques (the Delphi Curriculum).

Delphian School is a member of the Oregon Federation of Independent Schools (OFIS), an organization that works to limit government influence on school choice. The OFIS's current director, Mark Siegel, also acts as the school's assistant headmaster. The school is an accredited member of the Northwest Association of Independent Schools, and an accredited member school of Cognia, a standards-based accreditation body.

Delphian School's sports team is known as the "Dragons". The school participates in the Oregon School Activities Association's (OSAA) Northwest League, 2A classification, for girls and boys sports: basketball, tennis, cross country, track and field, boys soccer, volleyball, and cheerleading; and for such other activities as speech and debate, solo music, and choir.

Delphian School started its cheerleading squad in 2013. In 2016, they won the Class 3A/2A/1A state cheerleading title with an overall judged score of 160.70.

In 2014, the Delphian choir tied for the OSAA Choir State Championship. That year three school soccer players were named to the All-State team.

In 2018, Diego Martinez, a science mastery specialist at the Delphian School in Oregon, was among 11 teachers who participated in Space Center Houston's first-ever Space Center University for Atmospheric Research program.

At the 2022 Mountain Valley Conference district track and field championship the girls team won multiple disciplines including the 100 and 200 meters, 300 hurdles, and 4×400 relay. The boys team placed first overall, winning the 100, 200, 800, 1500 and 3000 meters, 300 hurdles, and the 4×100 and 4×400 relays.

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