In the Hong Kong Institute of Education (abbr. HKIEd), a vast amount of lesson plans for primary and secondary teaching practices are prepared by our pre-service teachers. These valuable documents are being wasted each year. One reason for this is that there are lack of formal mechanism to keep them. The other reason is that the non-standardization of these electronic documents prevents an effective exchange and retrieval of their contents. In this paper, a formal markup language for lesson plans is proposed and developed using XML. The formalization for the various components of lesson plans helps to foster a non-ambiguous data model. Using XML technology, not only we can relevantly query the lesson plans, we can display their contents in a variety of formats and styles using web-based technologies such as XSL and XSLT.