This study aimed to investigate the sustainability of an instructional design utilizing the novel approach of the Reflective Teaching Model for Reading Comprehension (RTMRC), and to continuously develop and validate instruments for reflective measures to ensure the sustainable teaching of reading comprehension. The RTMRC design was featured based on two main parts: the reflective teaching process (planning, acting, reflecting and evaluating) and the reading comprehension process (reader, strategy, text and task). Then, a quasi-experiment (the pre- and post-test control group design) was conducted with 168 grade-9 students to assess the performance of the RTMRC in practice. The reflective questionnaire was also applied as an instrument to gather feedback from students about the instructional context, with the aim of supporting the sustainable reflective practices of the teacher. The reading achievement in the experimental group was evaluated and fostered using this model. Through the analyses of t-tests and Cohen’s d effect size, it was found that the experimental group teaching with RTMRC outperformed the control group without RTMRC teaching. Using exploratory factor analysis, confirmatory factor analysis, Rasch analysis and testing measurement invariance across groups, we report that the instruments were found to be valid for measuring the effect of the RTMRC in teaching reading comprehension in English Language Teaching (ELT) in a sustainable manner.