This paper discusses the retrofit process of a classroom located in Antofagasta midtown, in Chile. Climate is desert coast climate, characterized by high solar radiation levels (both beam and diffuse radiation), as well as very high sky luminance (about 12.000 lm/m(2]) in the typical sunny day and more than 22.000 lm/m(2) in an overcast sky). Educational buildings in Chile are quite poor in terms of energy efficiency and comfort issues, but Government Agencies like AChEE - Chilean Agency for Energy Efficiency are working on the retrofit of this kind of spaces, because of the importance of education results on the predictable development of the Country. School of Architecture of the Catholic University of the North - UCN, is involved in the energy efficiency policies and research. As result of an internal research project, a case study classroom has been selected, monitored and simulated searching for the optimization of light and thermal performance. Users have been involved with questionnaires and educational results monitoring before the retrofit. Retrofit actions to take have been selected by computational simulation considering the following parameters: intensity and distribution of light, sun penetration profundity and glare probability. Simulation tools used in simulation are Ecotect, Radiance and DaySim. Final retrofit is currently on-going and results expected are an improving of more than 50 % in the ambient quality described with the considered parameters and a general satisfaction of final users. Better educational results of children are also expected as secondary result of the retrofit process.