Phonological awareness is the skill to access consciously to the structure of the spoken language. This implies recognizing and manipulating the phonological segments of spoken language. Numerous researches show that phonological awareness is critical in learning to read in alphabetic languages like Spanish. Therefore, stimulating the methaphonological skills development in pre-readers children and children who are beginning to read is very important. This article presents some of the results of an applied investigation designed to test a program to develop phonological awareness in 20 pre-school children and 18 first year elementary school students, who attend socially vulnerable schools in Concepcion, Chile. The part of the study which is reported corresponds to a quasi-experimental design with pre and post test based on Linguistic Segmentation Test (LST) by Orellana y Ramaciotti (2007), standardized for Chilean people. Treatment consisted in the development of 15 sessions with each participating group, using material specially designed by the researchers to train different aspects of phonological awareness. The results show positive effects of the intervention and confirm some aspects of the development of phonological awareness found in the literature. It concludes that it is possible to improve the children's methaphonological skills through the designed programme, which can be improved incorporating aspects that were not considerated originally.