This study investigates the efficacy of metacognitive strategy instruction and private speech promotion strategy instruction on the inferential and critical reading skills of middle school students, considering the role of working memory. While existing literature has established that general metacognitive strategies can enhance learning outcomes, such approaches may neglect content knowledge and inadvertently lead to a mechanistic application of strategies. Grounded in Vygotsky's cultural-historical theory, which posits that private speech plays an important role in cognitive development in subject matters, this research addresses a gap regarding the impact of private speech promotion on English reading comprehension. The study yielded several key findings. Firstly, students with higher working memory capacity demonstrated superior performance compared to their peers with lower working memory. Secondly, participants receiving strategy instruction exhibited significantly enhanced inferential and critical reading skills compared to those in a general instruction group. Notably, the private verbal facilitation strategy instruction group outperformed the metacognitive strategy instruction group in these areas. Finally, an interaction effect was observed between the types of str...