The complex learning and socio-emotional profiles of students who are twice exceptional are often accompanied by challenges to their identification and support in the primary school. This exploratory research project, conducted in a primary school in New South Wales, Australia, focused on developing and trialling a comprehensive and useful assessment tool for teachers to use in the preliminary stage of investigating whether students might be twice-exceptional. Using mixed methods research methodology and a Participatory Action Research design, three primary-school teachers (including the first author) developed the Teacher Checklist Questionnaire (TCQ) based mainly on published research and anecdotal findings. All teachers at the school site from Years 2 to 6 (N = 10) participated in the first trial of the TCQ and the results from the analyses were positive in terms of validity, reliability, and usefulness. The main conclusion is that the tool shows promise as an early investigative tool to assess twice-exceptional students.