Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
mainstreamed is an adjective meaning "(of the handicapped) placed in regular school classes". It carries one recorded sense.
(of the handicapped) placed in regular school classes
Definitions, synonyms and semantic relations for mainstreamed come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.