This paper presents findings from an action research project that investigated the application of Multiple Intelligences (MI) theory in classrooms and schools. It shows how MI theory was used in the project as a basis for suggestions to generate classroom practices; how participating teachers evaluated the project; and how teachers responded to the professional experience. Teachers reported successful student outcomes including more interest and motivation, better recall and deeper understanding, higher attainment, improved self-esteem, and more fun and enjoyable classroom experiences. For teachers themselves, the project was a challenge. They needed more planning time, more persistence, more collegiality, and more management support. All involved in the project found the experiment worthwhile, exciting, and a stimulus for radical change in their pedagogic practice and thinking. Teachers renamed and extended existing practices to include MI approaches and this led to a methodsshift and, ultimately, to indications of a mind-shift. It was apparent in the Irish MI Project that the premising of curriculum content and delivery, state certificate assessment, school organisational practices, and attitudes on a narrow, untenable and unfair construct of intelligence can result in educational exclusion and disadvantage for many students. Thus, it is suggested that the agency of intelligence in educational failure merits attention.