St. Mary's International School
🇯🇵 Tokyo · Founded 1954 · IB / American · Ages 5–18
A long-lineage Catholic, all-boys international school in Setagaya — one of Tokyo's most established and selectively accredited (CIS + WASC) IB Diploma providers.
Curricula
IB, American
Age range
5–18
Languages of instruction
English
Annual fees
SGD JPY 3,060,000–3,250,000
Enrollment
1,000
Boarding
No (day school)
IB authorised
DP
Accreditations
CIS, WASC
Tier Profile
We only tier dimensions backed by a public inspection verdict or verifiable accreditation. Other dimensions show a data flag — never a guessed score.
BrightKey's Assessment
St. Mary's International School was founded in 1954 and moved to its current 9-acre Setagaya-ku campus in 1971. It was established by the Brothers of Christian Instruction (the La Mennais brothers, a Catholic teaching order) and retains an explicitly Catholic identity, though families of all backgrounds attend.
It is one of Tokyo's defining single-sex international schools: an all-boys school of close to 1,000 boys from ~60 countries, spanning elementary, middle and high school (ages ~5–18). It is effectively the counterpart to Seisen International School (the long-established Catholic all-girls school in the same Setagaya area).
Academically, St. Mary's delivers an American-style college-preparatory curriculum across the lower and middle grades, culminating in the IB Diploma Programme in high school, with all six IB subject groups plus the TOK/CAS/EE core. English is the primary language of instruction.
Accreditation is a genuine differentiator: St. Mary's holds both CIS and WASC accreditation, plus EARCOS and JCIS membership. As with most Tokyo schools, it does not publish hard outcomes data (no IB average, pass rate, or destination lists).
Why These Ratings?
Inspection & AccreditationA — Excellent
Dual CIS + WASC accreditation — exceptional accreditation depth for a Japan-based school. Japan has no public inspectorate, so the tier reflects accreditation depth — A (S reserved for genuine inspection bands).
Strengths & Trade-offs
Strengths
- 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
- 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
Is It Right For You?
Best For
- ✓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
Not Ideal For
- ✕Families who want or require co-education
- ✕Families who need published outcomes/placement data before committing
- ✕Families dependent on documented, robust EAL/ESL support (provision not public)
- ✕Families seeking an AP / US-curriculum-only pathway (the diploma route is IB DP)
Curriculum
American-style college-preparatory curriculum from elementary through middle school, with the IB Diploma Programme in high school (all six subject groups plus TOK, CAS, Extended Essay). AP is NOT publicly documented; do not assume AP. No PYP/MYP authorization indicated.
Fees
Third-party aggregator lists 2026/2027 yearly tuition of approximately JPY 3,060,000–3,250,000 — school-reported via a third party, not independently confirmed on St. Mary's own fees page. Additional fees (registration, capital levy) are common and not captured here.
Admissions
All-boys; admission limited to boys. Entry points include reception and Grade 1 via OpenApply. Selectivity rates and specific criteria are not quantified publicly.
Campus Life
9-acre Setagaya campus; athletics (team 'Titans'), fine arts, a Liturgy programme reflecting the Catholic identity. Motto: 'A School with a Heart.'
University Placement
School-reported · not independently verified
Not public. No university destinations, placement statistics, or matriculation lists are published, though the school maintains a University Counseling function.
Sources
Every verifiable fact carries a public source — verify it yourself.
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