With the rapid changes in globalization and technology advancement, self-directed learning is argued repeatedly as a key competency needed to survive in the twenty-first century. In August 2019, the Taiwan Ministry of Education implemented the new "Curriculum Guidelines for 12-Year Basic Education." Being Taiwan's first official curriculum that promoted self-directed learning, this study contributed to the emerging knowledge of how the introduction of the curriculum guidelines affected students' readiness for self-directed learning. Three cohorts of high school students from seven schools returned 10,020 valid surveys. The Self-Directed Learning Readiness Scale (SDLRS), a reputable instrument developed by Lucy Guglielmino (2000), was used in the study. The results provided a bird's-eye view of evidence supporting our explanations for the positive, though slight, effect of implementing new curriculum guidelines in fostering self-directed high-school learners. Moreover, the progression of self-directed learning readiness appeared differently among schools and among different demographic associations. We suggest that future researchers both (a) qualitatively explore how specific latent variables were changed in different instructional interventions, and (b) conduct panel studies to advance our understanding of curriculum reform and learners' self-direction.