Nowadays, the enterprises that develop software have become strategic partners for their clients through value generation, by delivering products that support different business processes. However, there are still problems in software developing projects, like quality. This paper describes the results of the implementation of a quality assurance model that integrates CMMI (Capability Maturity Model Integration), TSP (Team Software Process) and PSP (Personal Software Process), with the objective to improve the quality of the process and of the software product delivered. The research methodology is a quantitative one, and the investigation design is quasi-experimental about pre-test and post-test. A total number of 22 software projects have been selected to evaluate the model improvements. The results show that there are important improvements in reducing the quality costs and the number of defects. At the same time, the project profitability and customer satisfaction is also increased.