Whereas many pre-intermediate and intermediate level students of English as a Foreign Language (EFL) might benefit from receiving detailed feedback on mistakes in their written compositions, there are obvious practical limits to the amount of corrective feedback that teachers in schools and universities can provide. This article briefly describes the Universidad Nacional de Educacion a Distancia's computerized grammar checker for pre-intermediate and intermediate level Spanish mother-tongue students of EFL. The main part of the article details how a student, working with the grammar checker and independently from teachers, detected and corrected mistakes in her own composition. In the light of this and other trials it was decided to publish the Grammar Checker. The trials also showed how the Grammar Checker can be improved and developed. Brief reference is made to its possible impact on the ways in which foreign languages are taught and learnt. (Contains 1 figure.)