This study examines the effects of schools' implementation of a new system for testing on student reading. Data on seven Norwegian primary schools were obtained through participant journals and interviews conducted throughout a period of five years. The analyses draw upon Cultural-Historical Activity Theory, especially the framework for expansive learning and contradictions. The findings reveal several discursive struggles in the interactions between the principals and teachers during the developmental process. The data analysis indicates that the initiatives to implement testing as a collective school practice were underlain by tensions concerning student learning (e.g. individual vs. collective testing), and teachers' working conditions (e.g. individual vs. collective practice). Even though these tensions are short-term, they are part of a long-term activity and point to the need to address questions of leadership in schools. Revealing such tensions can help leaders defuse such strained conditions and improve learning.