The main objective of this article is to demonstrate with the help of learner corpus data the practical relevance of the phraseological dimension of language for writing assessment in higher education. Phraseological competence is now widely recognized as an important part of fluent and idiomatic language use, but its development has not received the attention it deserves in the CEFR. The study investigates the development of linguistic correlates of syntactic, lexical, and phraseological complexity in learner texts at B2, C1, and C2 and shows that while no measure of syntactic or lexical complexity seems to have an impact on human raters' overall judgement of writing quality, two measures of phraseological complexity explain 25% of the variance in the data set. Results suggest that incorporating phraseological competence into the scoring rubrics of university entrance language tests would help language test developers add construct validity to language assessment in higher education. More generally, this study also shows the crucial role that Language for Specific Purposes learner corpora could play in language assessment.