Situated evaluation views learning as a phenomenon which occurs in socioculturally specific contexts (Bruce and Rubin 1992). Its proponents recognize two forms of curriculum: one is a documented version, which proposes idealized teaching practices across various teaching situations; and the other is a realized version of curriculum implementation in actual classrooms. This paper explores how communicative language teaching (CLT) is understood and implemented by Japanese secondary school English teachers. In order to understand the successes and failures of curriculum implementation, we need to examine it in real contexts. The longitudinally collected data suggest that teachers have difficulty in integrating CLT and form-based instruction, although documented instructional goals imply a smooth integration of the two. Teachers also report that implementation of CLT is not simple because of various situational constraints.