This paper reports on a case study investigating students' participation and learning presence in an educational blog implemented as a cross-thematic inquiry activity exploring and debating on the acid rain problem. Twenty-one secondary education students (14-15 years aged), coming from two separate classes, were involved. The content and commentary postings of the blog were analysed using a combined framework, combining the model of Community of Inquiry (CoI) and the representation of learning mapping, aiming to reveal students' engagement in blogging activities. The analysis shed light into the different patterns of participation that students showed and their gradual evolution of learning presence which supported the development of a CoI. The results suggested that properly designed blog activities can help students to achieve higher cognitive levels through enhancing their collaboration skills and critical thinking. The findings showed that the proposed framework could be of value for the design of blog-based instructional practices and ongoing research in the field. (Contains 6 figures and 4 tables.)