P. Moorman, and E. Johnson. Proceedings of the 8th annual conference on Innovation and technology in computer science education, page 193--197. New York, NY, ACM, (2003)
P. Sivilotti, and S. Laugel. Proceedings of the 39th SIGCSE technical symposium on Computer science education, page 291--295. New York, NY, USA, ACM, (2008)