The document proposes an approach for developing educational software based on Activity Theory to address the lack of methodologies in this area. It analyzes how Activity Theory can help describe educational activities and guide software development. It then presents a case study of developing games about a park using the Cocoa software to demonstrate applying the analysis of the educational activity and computational artifact. The major conclusions are that the proposed approach addressed important aspects of educational activities and helped organize Constructionism concepts while raising questions to further the research.