The article reports on the efforts to establish a secondary school, set up within the free school legislation, to be comprehensive, serving the diverse population of the city in which it is located. This was achieved through a policy which admitted students from four 'nodes' across the city and gave priority to children with special educational needs and looked-after children, and by teaching the children in mixed-attainment classes. We report selected findings from a research project which followed the school's progress from the original application to be a free school to its establishment with a full complement of students, and which included interviews with teachers, senior school staff, professional service staff, governors, parents and students. We discuss the background and impact of the admissions policy and the practice of mixed-attainment schools, both unusual in England. We also consider some of the challenges and limitations for a school choosing to operate in this way within an education system which strongly emphasises individual performance and competition between schools.