Understanding the object of learning is a significant, yet often elusive, part of analysing a lesson through the lens of variation theory of learning. It involves not only specifying the usual learning objectives in terms of content and how to handle it, but also through identification of critical aspects to be discerned. The role of critical aspects in formulating the object of learning in an elaborate and useful way is the focus of this discussion paper. This is explored by comparing two mathematics lessons in China, designed and conducted by two teachers skilfully with bianshi pedagogy. As the content, textbook resources and students’ characteristics are basically the same, the subtle difference in the observed objects of learning becomes apparent. This difference is reflected in two contrasting sets of critical aspects that are structuring the lessons. In Marton (2015), “the object of learning is described primarily in terms of critical aspects and features to be discerned” for a better precision. Our analysis may contribute to a further discussion about how far the critical aspects constitute the meanings behind the content, which is not commonly addressed when a lesson is mainly analysed in terms of patterns of variation in a mechanical manner.