Through the qualitative interviews of five implementers of primary school mathematics curriculum, this study addresses the ways in which mathematics lessons are evaluated. Results show that each evaluator recognizes different aspects of a "good lesson," however, among all criteria, the design of the lesson plan, realization of the lesson goals, active student participation, and mathematical thinking are seen as key indicators in lesson evaluation. The study also shows that student performance is a major point of concern in lesson evaluation, and some extreme teaching practice has drawn attention and being reflected by some implementers of the New Mathematics Curriculum.