There is a consensus that case studies in Business English class are helpful to foster critical thinking, but little research has been done to explore how case studies facilitate it. To bridge the gap, the present study uses the revised Bloom’s taxonomy as a tool to qualitatively and quantitatively investigate the effect of case studies in Market Leader textbooks on fostering critical thinking based on cognitive load theory. First, the presence of six cognitive levels targeted in the tasks is examined to see how case studies sequence their tasks according to the increase of cognitive complexity. Secondly, the scaffoldings distributed across the sequential tasks are explored to investigate how well they impose appropriate amount of cognitive load on students. Although six cognitive levels are found, there is an inappropriate administration of task scaffolding in a single task or task chain, leading to insufficient or superficial scaffolds and thus inducing high level of cognitive load for students to develop critical thinking. Accordingly, case study writers and teachers are recommended, when designing and adapting sequential tasks, to consider systematic inculcation of cognitive levels among tasks and proper administration of scaffolding with regard to the aspects of task input, conditions, progress and outcome so that a balanced level of cognitive load aligned with the state of working memory capacity of students can be achieved for fostering critical thinking.