He was hit near the Cos Cob station at 12:01 a.m. Sunday by a southbound train that departed New Haven at 10:45 p.m.
Greenwich school officials offered condolences as they identified the boy as a junior at Greenwich High School, but did not immediately release his name.
The name of the victim has not been released as the Metropolitan Transportation Authority continues to investigate, Metro-North spokesman Shams Tarek said.
Police said he was a student at Greenwich High School, according to NBC Connecticut, which said mental health staff will be available for students Monday.
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