Promoting students' conceptual understanding and academic language development is a primary goal of instructors in all subject areas. These goals, however, are sometimes hindered by the way students' learning is assessed. In many college-level courses, knowledge-level tests that assess concrete thinking associated with superficial approaches to teaching are frequently used. Rubrics used to grade short open-ended responses often have vague criteria subjectively applied to a rating scale. To address these issues, this paper uses a new lens, shaped from the ideas of Vygotsky, a cultural-historical theorist, for understanding the development of academic language use (in Vygotskian terms, thinking that demonstrates conceptual understanding) and its assessment. Vygotsky's stages of concept learning are applied to form criteria on a short-answer response rubric. Examples of students' academic language use according to developmental level are provided. Recommendations for the adaptation of this type of classroom assessment for use in other courses are made, along with suggestions for future research.