The student´s screening made by schools corresponds to a regulatory mechanism for school inclusion and exclusion that normally overlaps the parental expectations of school choice. Based in "Parents survey 2006" data (n=188.073) generated by the Chilean Educational Ministry, this paper describe the parents reasons for choosing their children's school, and school´s criteria for screening students. It concludes that the catholic schools are the most selective institutions and usually exceed the capacity of parental choice. One of the reasons to select students would be the direct relationship between this practice and increasing the average score on the test of the Chilean Educational Quality Measurement System (SIMCE).