Understanding how blogs can support collaborative learning is a vital concern for researchers and teachers. This article explores how blogs may be used to support secondary education students' collaborative interaction and how such an interaction process can promote the creation of a Community of Inquiry to enhance critical thinking and meaningful learning. A science case-based project in which 15 secondary students participated was designed, implemented and evaluated. Students worked on the science blogging project for four months. Students were asked to be collaboratively engaged in purposeful critical discourse and reflection in their blogs in order to collectively solve science challenges and construct meaning about topics related to astronomy and space sciences. Through student comments posted in the blog, the findings showed that the blog environment afforded the construction of a Community of Inquiry and therefore the creation of an effective online collaborative learning community. In student blog comments, the three presences for collaborative learning took place: cognitive, social, and teaching presence. Moreover, this research found a positive correlation among the three presences--cognitive, social and teaching--of the Community of Inquiry model with the level of learning obtained by the students. This article discusses a series of issues that instructors should consider when blogs are incorporated into teaching and learning. It is claimed that embedded scaffolds to help students to argue and reason their comments in the blog are required to foster blog-supported collaborative learning.