New Public Management reforms have been argued to intensify the use of strategic management in public organizations, but there is a need to understand how reforms influence specific aspects such as strategy processes and strategy content. The NPM reforms are expected to formalize and professionalize strategy processes and strategy content towards greater competitiveness, but this may counter cooperation between organizations, which is essential in many areas for overall service provision. Research has provided little empirical knowledge about the simultaneous competition and cooperation in the public sector. This study offers such knowledge via a panel case study of five Danish upper secondary schools over a ten‐year period during a large NPM reform. The study includes three rounds of interviews with school principals before, during and after the reform, combined with secondary data. The study shows that, during reform implementation, strategy processes become more formalized and professionalized, and that teachers, in particular, lose influence. Regarding strategy content, the authors find an increase in external focus and competition, though schools maintain a focus on cooperation. The results suggest that NPM reforms can significantly change strategic management in public organizations, and that this is not necessarily at the expense of cooperation, at least in the short run.