Knowledge elicitation is a critical problem in computerized learning environments that make use of a knowledge base. Fortunately, contrary to usual expertise elicitation situations, didactic scientific knowledge is quite often well formalized, and authors are used to deal with the logical organization of the domain they teach. We want to propose here an original tool, a logical spreadsheet which, if included in an authoring package, will help authors organize concepts and at the same time make both conception and maintenance of didactic knowledge bases much easier.