This article presents Apex, a system that can automatically assess a student essay based on its content. It relies on Latent Semantic Analysis, a tool which represents the meaning of words as vectors in a high-dimensional space. By comparing an essay and the text of a given course on a semantic basis, our system can measure how well the essay matches the text. Various assessments are presented to the student regarding the topic, the outline and the coherence of the essay. Our experiments yield promising results.