This paper examines dynamism in students' situational willingness to communicate (WTC) within a second language classroom. This longitudinal study involved twelve English as a Second Language (ESL) participants who enrolled in an English for Academic Purposes (EAP) programme in New Zealand for five months. Based on data from classroom observations, stimulated-recall interviews and reflective journals, the in-depth analysis of a case study reveals that learners' situational WTC in second language (L2) classes could fluctuate and dynamically change over time. This involved a process where situational WTC was jointly affected by learners' cognitive condition and linguistic factors, together with classroom environmental factors. The in-depth qualitative analysis of a single case in individual lessons allowed us to see the dynamic nature of WTC.