This paper provides an overview of the advances on web mining in the domain of education by categorizing research on the field using the web-mining taxonomy: web content, web usage and web structure mining. Previous reviews focused on data mining methods applied to data derived from educational software applications (web based or not) and institutional administrative systems as well as from data gathered in typical classroom environments. The overview focuses on knowledge acquired from web based educational environments and the open web. More specifically it addresses: a) applications that dynamically update their content by extracting relevant educational information from the open web in order to meet user specific needs, b) applications that extract knowledge from usage data coming from educational web-based environments, and, c) applications that obtain knowledge coming from structure data such as links or social network connections that exist in e-learning applications and the open web.