A method and an apparatus for teaching through assessment-directed individualized instruction using a series of interrelated interactive and linear lessons on a computer or computer network. In an embodiment, subject matter is broken into dependent and independent skills and concepts. Students are presented the skills and concepts in skill/sub-skill teaching cycles that incorporate concept-teaching activities, guided practices, independent practices, and assessments. The progress of the student is tracked in a knowledge base. The teaching of each student is customized based upon the level of understanding of each skill and concept. In an embodiment, the student is allowed to proceed even though the student has not achieved a predetermined level of understanding of past skills and concepts as these concepts will be re-introduced over time based upon evaluations of the knowledge base as needed until mastery is developed.