This chapter presents an empirical assessment of the quality of the process of building software systems in light of the recent emergence of agile development methodologies, which were designed to to help with the development of higher quality information systems under given conditions. The purpose of this research was to assess one of these agile approaches, eXtreme Programming (XP), through a comparison with a traditional (design-driven) software construction process. With this aim we observed and measured the work of several student groups using different approaches to produce software for commercial companies during a semester. The data collected were analyzed following the Bayesian approach. Our results indicate that that XP could cope with small/medium size projects of software construction delivering a measurable improvement in the quality of the system as judged by the business clients.