How creativity in education is applied by teachers to secondary school contexts is dependent on how the term 'creativity' is grounded, politicised, and practised. This paper reports on an international study of secondary schools in Australia, USA, Canada, and Singapore investigating how creativity is understood, negotiated, valued and manifested in secondary schools, focusing on teacher and student understandings, actions, benefits and impediments to creative and critical thinking. Participant reflections revealed inter-, trans- and cross-disciplinary learning shaped by teacher collaboration, dialogue and classroom organization that fosters critical and creative thinking. Implications are made for the ways practicing teachers develop and foster creativity via pedagogical approaches that enhance connectivity and interdisciplinarity of teaching practices between domains of learning. An education-based Creativity Index through which administrators and teachers can gauge, assess and implement creative skills, capacities, pedagogic practices and assessment of creativity within secondary schools is posited. Implications for STEM/STEAM education and centralizing creative capacities in teaching, learning, and educational change are offered.