學校改進是複雜而帶有目標的活動，要靠能動者發揮其潛能和創意，以互利的態度協作來增強學校的發展能量。本文以「活動理論」中的「活動三角形式」為綱，並以香港「優質學校改進計劃」的校本改進工作為例，探討該計劃的主要能動者──「學校發展主任」和「借調教師」──在學校開展改進工作的歷程。文章試圖透過描述能動者的工作特性和實踐經驗，展示學校改進其實是一種延展性的學習活動。

School improvement warrants a complex series of activities with clear objectives. The success of school improvement depends on the ability of change agents to enhance the capacity of client schools with creative energy and an attitude that ensures mutual benefits. This article depicts the work of the Quality School Improvement Project from the perspective of Vygotsky’s activity theory. By focusing on the dynamics generated from an “activity triangle,” the discussion explores the roles and functions of active change agents in the school improvement endeavor, i.e., School Development Officers and seconded teachers. The experience of change agents suggests that school improvement is a kind of mediated learning activity that stretches the change capacity of all participants.