The importance of collocations, i.e. idiosyncratic binary word co-occurrences in the context of second language learning has been repeatedly emphasized by scholars working in the field. Some went even so far as to argue that "vocabulary learning is collocation learning" (Hausmann, 1984, p. 395). Empirical studies confirm this argumentation. They show that the "collocation density" in learner corpora is nearly the same as in native corpora, i.e. that the use of collocations by learners is as common as it is by native speakers. At the same time, they also find that the collocation error rate in learner corpora is about 32% (compared to about 3% by native speakers). A CALL-based collocation writing aid could help learners to better master collocations. However, surprisingly little work has been done so far on collocation learning assistants. We propose a collocation writing assistant for American English learners of Spanish which may be used as checker of both isolated collocations and collocations in texts. In addition, it offers the possibility to actively explore and administer collocation resources. [For full proceedings, see ED564162.]