L1 grammar education is internationally criticised because of its pedagogy and its curriculum content. There is a gap between linguistic theory and school grammar in which the latter rarely makes use of possibly relevant insights from the former. At the same time, linguistics itself has never seriously undertaken attempts to identify the fundamental, theory-neutral conceptual knowledge of the field. Instead, most linguists spend time on defining the boundaries between different linguistic theories, making it harder for language teachers to take advantage of insights that linguistics has to offer. This paper, therefore, aims (1) to establish a theory-neutral foundation for sentential syntax and semantics and (2) to explore the role this foundation should play in language education according to linguists. The experts were asked to articulate the most important linguistic concepts for both the domain of linguistic theory and the domain of grammar education. Twenty-six concepts were identified and ranked in a Delphi study for relative importance in both domains. The importance of the concepts correlated strongly for both domains, making it feasible to bridge the gap between linguistics and school grammar. The Dutch context is taken as a frame of reference, although the study's relevance is likely to be broader.