When teaching grammar, one of the biggest challenges teachers face is how to make their students achieve conceptual understanding. Some scholars have argued that metaconcepts from theoretical linguistics should be used to pedagogically and conceptually enrich traditional L1 grammar teaching, generating more opportunities for conceptual understanding. However, no empirical evidence exists to support this theoretical position. The current study is the first to explore the role of linguistic metaconcepts in the grammatical reasoning of university students of Dutch Language and Literature. Its goal was to gain a better understanding of the characteristics of students’ grammatical conceptual knowledge and reasoning and to investigate whether students’ reasoning benefits from an intervention that related linguistic metaconcepts to concepts from traditional grammar. Results indicate, among other things, that using explicit linguistic metaconcepts and explicit concepts from traditional grammar is a powerful contributor to the quality of students’ grammatical reasoning. Moreover, the intervention significantly improved students’ use of linguistic metaconcepts.