The pre-first grade kindergarten students have opportunities to participate in dance classes after school.
The Seisen After School Activities program (SASA) for elementary students runs for about two ten week sessions, one before Christmas and one after. Each activity usually lasts one hour from 3:30 pm. Activities offered by teachers have included pottery, T-shirt design, cookery, jazz and tap dance, calligraphy, art, painting, crafts, origami, netball, tennis, dance, computer, guitar, Spanish, French, and quilting.
Seisen takes an active role in all fine arts competitions and festivals for students in grades 7-12. Secondary school after-school activities include debate, speech, drama, brain bowl, MUN (Model United Nations) and math field day. Students who participate in co-curricular academic teams are eligible for academic letters and letter jackets.
Junior High and High School sports offered include: tennis, volleyball, cross country, swimming, basketball, soccer, badminton, and track and field. Ping-pong is offered as an optional weekly activity. Students participating on Varsity or Junior Varsity teams are eligible for a Varsity or Junior Varsity Letter.
Seisen competes with other international schools and U.S. Military schools as well as Japanese schools. Seisen participates in the Kanto Plains league for tennis, volleyball, soccer, basketball, cross country, and track and field. The teams are supported by the Girls Athletic Association (GAA).