This paper presents the design of eLeTK, which is a software system that may be used for enhancing on-line educational environments. The main concept introduced in this paper is represented by educational data/knowledge flow. The data flow is transformed into a knowledge flow provided that all input data represents activity produced by an on-line educational environment. On the other hand, the output of the software system is redirected towards the educational environment in an attempt to enhance its capabilities. eLeTK may become a recommender system for students or professors, a knowledge self-assessment tool for students or an custom learning path builder. The core business logic of eLeTKis represented by custom integration of different machine learning algorithms adapted to work with data provided by online educational environments.