Seisen International School vs St. Mary's International School
🇯🇵 Tokyo · Side-by-side comparison on verifiable public data.
Neither Seisen International School nor St. Mary's International School sits in a market with a public inspectorate, so both are assessed on verifiable accreditation, curriculum authorisation, and published data rather than an official quality rating. Both are day schools with fees in the same market band — see the table below for the figures, and verify against each school's own published fees.
Key Facts
| Seisen International School | St. Mary's International School | |
|---|---|---|
| Curriculum | IB | IB / American |
| Ages | 2–18 | 5–18 |
| Languages of instruction | English | English |
| Annual fees | JPY 2,650,000–2,850,000 | JPY 3,060,000–3,250,000 |
| Enrollment | 695 | 1,000 |
| Boarding | Day only | Day only |
| Accreditations | CIS, NEASC, JCIS | CIS, WASC |
Strengths
- ✓Full IB continuum (PYP + MYP + DP) under one roof — strong vertical academic coherence
- ✓Strong dual international accreditation: CIS + NEASC, plus JCIS membership
- ✓Long-established (since 1962) with a clear, distinctive Catholic, girls'-school identity
- ✓Documented EAL support plus dedicated learning-support specialists
- ✓Small class sizes (average ~20) and a low reported student-faculty ratio
- ✓Dual CIS + WASC accreditation — exceptional accreditation depth for a Japan-based school
- ✓Full K–12 continuity (ages ~5–18) on a single 9-acre campus, with IB DP capstone
- ✓70-year-old established institution with a clear, stable Catholic mission
- ✓Strongly international student body (~1,000 boys, ~60 nationalities)
- ✓Published, transparent IB DP subject offering (all six groups + TOK/CAS/EE)
Trade-offs
- !IB Diploma results / average scores are not published — academic outcomes cannot be independently verified
- !Tuition is not published on the official site; fee data is third-party (school-reported) only
- !Single-sex from Grade 1 onward excludes boys beyond kindergarten
- !Catholic sponsorship may not suit families seeking a fully secular environment
- !No boarding — day-school only
- !No published academic outcomes — IB average, pass rate and university destinations all not public
- !EAL/ESL support is not described anywhere public; English-language-learner provision is unverifiable
- !AP is sometimes assumed but is NOT publicly evidenced — only the IB DP is confirmed
- !Official tuition figures could not be confirmed on the school's own fees page (third-party only)
- !The school's Wikipedia entry references 2014 historical abuse allegations — a matter of public record families may wish to research independently
Best Fit For
- • Families seeking a single-sex environment for girls within a rigorous IB pathway
- • Families who value a faith-rooted (Catholic) ethos with cultural/religious inclusivity
- • Younger families wanting a co-ed start in kindergarten that transitions to girls-only
- • Students needing EAL support entering an English-medium IB programme
- • Families specifically seeking a single-sex, all-boys environment
- • Families wanting a Catholic / faith-based education within an international setting
- • Families prioritising accreditation rigour (CIS + WASC) as a quality signal
- • Long-stay expat or local families wanting K–12 continuity in one institution
University Placement
School-reported · not independently verified
School-reported, unverified: Seisen reports that 98% of graduates proceed to a higher educational institution. No specific university-destination lists or IB score averages are published.
Not public. No university destinations, placement statistics, or matriculation lists are published, though the school maintains a University Counseling function.
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Frequently Asked Questions
Should I choose Seisen International School or St. Mary's International School?
Seisen International School is best for: Families seeking a single-sex environment for girls within a rigorous IB pathway. St. Mary's International School is best for: Families specifically seeking a single-sex, all-boys environment. The right choice depends on target curriculum, budget, and family priorities — the two are not linearly comparable.
How do fees compare between Seisen International School and St. Mary's International School?
Seisen International School: JPY 2,650,000–2,850,000. St. Mary's International School: JPY 3,060,000–3,250,000. Verify against each school's own published fees; some figures are sourced from third-party aggregators.
What curricula do Seisen International School and St. Mary's International School offer?
Seisen International School: IB. St. Mary's International School: IB, American.
Do Seisen International School or St. Mary's International School offer boarding?
Seisen International School: day school only. St. Mary's International School: day school only.
This comparison is BrightKey's independent assessment using verifiable public data only. University-placement figures are school-reported and not independently verified. BrightKey takes no payments from schools. Our method →