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Seisen International School — Coeducational Only at Kindergarten

Tokyo, Japan

A Catholic girls' school with a coeducational Montessori kindergarten, running the full IB continuum (PYP/MYP/DP) from Grade 1 onward.

Researched by William Prep from published sources. Not yet verified by the school. — Last reviewed by William Prep: 2026-09-24

Seisen was founded in 1962 by the Handmaids of the Sacred Heart of Jesus. Its Montessori kindergarten is coeducational; from Grade 1 onward it is reportedly a girls-only school running the full IB continuum (PYP/MYP/DP).

At a Glance

Coeducation	Coed kindergarten only; girls-only Grade 1–12 (not independently confirmed)as of: 2026-09-24
Curriculum	Full IB continuum (PYP/MYP/DP) (not independently confirmed)as of: 2026-09-24
Enrolment	≈700 (40+ countries) (not independently confirmed)as of: 2026-09-24
Est. First-Year Cost (G1–5)	≈¥3.83M2026-27 · as of: 2026-09-24

Coeducational Only at Kindergarten — a Real Constraint for Families With Sons

Seisen's Montessori kindergarten is coeducational, but Grade 1 onward is girls-only. That means a family with a son enrolled at the Seisen kindergarten needs to plan a transfer before Grade 1 — a structural fact that directly shapes school choice, not something a generic "international school" label would tell you.

William Prep’s Analysis

For families hoping to keep one child at one school from kindergarten through graduation, this is the first thing to check before applying — not something to discover after enrolling. For families actively seeking a girls-only environment from Grade 1 onward, the same structure is a point in the school's favor rather than a caveat.

Fees: A Real First-Year Total of About ¥3.83M (Grade 1–5)

Seisen's own 2026-27 fee schedule lists three non-refundable one-time charges: a ¥30,000 application fee, a ¥300,000 registration fee, and a ¥700,000 land and building development fee. On top of that, an annual ¥150,000 building maintenance fee applies alongside grade-banded tuition (¥2,650,000 for Grade 1–5). Added together, a genuine first-year total comes to roughly ¥3,830,000. IB exam fees (¥20,000/subject) and the school bus (¥310,000 one-way / ¥420,000 round-trip) are separate.

University Entrance Eligibility in Japan

School-accreditation route	Yes (not independently confirmed)
Student-qualification route (IB, etc.)	Yes

The CIS/NEASC accreditation is based on third-party reporting, not confirmed against either registry directly this session. Independent of that, a student completing the full IB Diploma qualifies via the individual-credential route regardless.

Fees & Estimated First-Year Cost

academic year: 2026-27

Application Fee	¥30,000
Registration Fee	¥300,000
Land and Building Development Fee	¥700,000
Building Maintenance Fee	¥150,000
Tuition (Grade 1–5)G1-G5	¥2,650,000
Tuition (Grade 6–8)G6-G8	¥2,700,000
Tuition (Grade 9–12)G9-G12	¥2,700,000
Estimated First-Year Total	¥3,830,000

Includes: application, registration, capital, facilities, tuition — Excludes: Excludes school bus, IB exam fees (¥20,000/subject), the Grade 12 graduation fee, and iPad costs. This uses Grade 1–5 tuition as the base.

What Makes This School Distinctive

A coeducational Montessori kindergarten inside a girls' school

Boys and girls both attend kindergarten; only girls continue into Grade 1

Reported as, since July 2020, the first all-girls IB continuum school in Japan.

Families with sons need to plan for a post-kindergarten transfer from the moment they enroll, not discover it later.

Admissions

Cycle

未確認（Grade 1–11は英語・算数試験と家族面接あり） (not independently confirmed)

What Japanese Families Should Know

Who Might Find This School a Good Fit

Might suit — Families wanting a girls-only environment continuously from Grade 1 through graduation

Might not suit — Families wanting to keep a son at the same school past kindergarten (a transfer becomes necessary)

William Prep’s Analysis

What matters most in researching Seisen is how much a single yes/no "is it coeducational?" question can obscure — the real answer depends entirely on grade level, and that's exactly the kind of nuance a family needs before applying, not after.

Questions to Ask the School

1.What is the current status of the CIS and NEASC accreditations, and when is the next review?
Why this matters: Not confirmed against either registry directly this session.
2.What is the IB DP average score, and where do graduates matriculate?
Why this matters: Not confirmed this session.

Sources & Verification

Tuition & Fees — Seisen International Schoolprimary source · as of: 2026-09-24Fetched directly. 2026-27: application ¥30,000, registration ¥300,000, land/building development ¥700,000 (one-time), building maintenance ¥150,000/yr, tuition by grade band.
Search synthesis on Seisen history and accreditation — Multiple (incl. Wikipedia, seisen.com/60th)third-party source · as of: 2026-09-24Founded 1962 by the Handmaids of the Sacred Heart of Jesus. Coeducational Montessori kindergarten, then girls-only Grade 1-12. CIS/NEASC accredited; IB World School (PYP/MYP/DP) and, as of July 2020, reported as the first all-girls IB continuum school in Japan. ≈700 students, 40+ nationalities. Not independently confirmed against seisen.com's own accreditation page this session.
大学入学資格について — 文部科学省 (MEXT)official source · as of: 2026-09-23Sets out the routes to 大学入学資格: MEXT-designated schools; graduates of 12-year programmes at institutions accredited by WASC, CIS, ACSI, NEASC, Cognia or COBIS; holders of the IB Diploma, Abitur, Baccalauréat, GCE A-Level, International A-Level or European Baccalaureate; 高等学校卒業程度認定試験 (age-18 gated); and individual university review at 18+.

Last reviewed by William Prep: 2026-09-24

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