Current e-learning systems do not offer content customized for sophisticated learner characteristics. Different learner types are supported only by means of varying presentation styles. Methods for specifying learner-centered learning process are missing. For providing the right learning content in a proper context, in the right dosis and in the right moment, an e-learning system must follow the changes of learner's cognitive structures. This work presents SiteLang::Edu, a formal approach to specifying the learning process according to Piaget's constructivistic theory. The approach allows to specify the learning process for learners with different learning styles. SiteLang::Edu specifications can be validated thanks to the operational semantics.