The BLITS system described in this paper is a casebased system designed to help users draft effective business letters in English. The typical end user has at least a secondary school education, is computer literate, and knows the English one learns at school or university (how to write correctly, but not how to write effectively). The learning support offered by BLITS is based on two modern educational approaches: constructivism and self-directed learning. BLITS does not teach "rules" for writing effectively and does not offer step by step training in converting ideas and intents into a well-written letter. On the contrary, the system leaves it up to users to make judgments of what effective writing means in a given situation, taking into consideration a number of suggested alternatives and the results those texts obtained in previous correspondence. It is therefore the development of the learner’s judgment -- the capacity to choose words judiciously instead of applying rote formulas -- that makes working with BLITS, like all constructivist-inspired learning aids, a truly educational experience.