St. Mary's International School

An all-boys Catholic K-12 in Setagaya, founded by the Brothers of Christian Instruction in 1954 and one of the longest established international schools in Tokyo. A leading option for families set on a boys' school with strong academic outcomes.

St. Mary's runs an American programme that culminates in the IB Diploma, with consistent IB averages around 35 to 37 points and pass rates over 90 percent. About 1,000 boys from more than 50 nationalities attend on the Setagaya campus, which the school moved to in 1971. Uniform is mandatory and the tone leans more traditional than the comparable co-ed schools, with explicit weight given to service, integrity and the formation of gentlemen.

The campus shares geography and shuttle logistics with Seisen, which makes mixed-sibling planning straightforward. Catholic identity shapes the ethos, but Mass and religious practice are voluntary and the student body is mixed. First year costs run high once one-off fees, bus, uniform and devices are added in, and tuition sits at the top end of the Tokyo market.

• All-boys K-12 Catholic IB school in Setagaya, founded 1954 by the Brothers of Christian Instruction. One of Tokyo's "big four" international schools.
• IB DP outcomes are the headline. Pass rate consistently above 90%, average score 35,37 against a world average around 30, with strong physics and maths HL performance.
• Strict tone. Uniform, blazer and tie, and an explicit "gentlemen" framing that families compare unfavourably with more relaxed peers like YIS.
• EAL support stops early. Available through Grade 8 only, limited in 9,10, none for entrants into Grade 11. Near-native English required for upper-school admission.
• Historic abuse case is the elephant in the room. Multiple allegations against members of the religious staff covering the 1960s,70s came public in 2014, including one Brother who confessed to raping a student. Coverage continued through 2019 around silencing of victims in Japanese Catholic institutions.
• A commenters, citing similar cases at peer schools, frames Tokyo international-school abuse cases as historically under-reported because of light regulatory oversight and short expat tenures.
• Parent-survey signal from the school side: roughly 80% rated academics strong or very strong in a 2013 poll. Strong alumni profile, including Japanese music figures from m-flo.