In the literature about children syntactic development, particularly during last four decades, it's been frequently read that studies sustain on spontaneous speech samples, i.e., daily dialogic instances between children or between children and adults, are problematic because it's necessary to have a considerable amount of children talk to pick up the syntactic forms in study and carry out a statistical analysis (Demuth, 1996). Besides some studies consider that samples does not represent child language uses but some specific usages (Chomsky, 1969), and so the results lacks of validity and are only descriptions of syntactic tendencies (Lust, Flynn, & Foley, 1996) or that the data are spurious because in spontaneous contexts is difficult to control the interference of contextual variables (Echeverría, 1978). However there is consensus about the fact that these samples provide rich qualitative data. In order to pose an alternative to this methodological controversy, this paper presents a semi-structured interview design that seeks to preserve the distinctive characteristics of conversational exchanges but allows obtaining a sizeable amount of children syntactic data, to make a comparison between subjects and statistical processing. The design takes into account the contributions of a group of cognitive perspectives about the processes by which the subjects produce, comprehend, acquire, and develop language: Cognitive Linguistic (Lakoff, 1987; Langacker, 1987), Mental cognitive frames and Spaces Theory (Fauconnier, 1985), Gramaticalization Theory (Hopper, 1998), and Language Usage Model (Toma sello, 2001). Also it considers some methodo logical criteria from Sociolinguistics (Labov, 1991; Lavandera, 1984), Ethnography of speaking (Gumperz, 1982), Functionalist perspective on language development (Karmiloff-Smith, 1986), and a set of criteria developed in a previous ex- ploratory research (Silva, 2001). We select interview because it's recognized that it's the situation which best reproduces the characteristics of everyday conversational interactions (Labov, 1991) and in it subjects (children or adults) tend to provide more information to a skilled interviewer than in questionnaires. We formulated a set of criteria that prevent reproducing experimental circumstances (i.e., children feel self-conscious and evaluated) and thus enable children to interact with the interviewer in the most natural and spontaneous way as possible. The results obtained by Silva (2008) provided empirical support to the effectiveness of the methodological instrument developed. The aim of the study was to identify and describe the different forms of Relative Clauses (Rcs.) produced by two groups of children of 5 and 7 years in adult-child interactions. Considering the particular purposes of this research adaptations were made to the classical interview. The first adaptation was to convert the interview into a semi-structured interaction. With this technique we could obtain sizeable children autonomous speech and functional uses of Rcs. The instrument promotes children productions of discursive sequences by focusing the interaction on different significant childhood topics. So we had to identify, in a preliminary screening study, the discursive nuclei in the children communities. With the semi-structured interview we were able to collect 860 Rcs. and identify seven different types of Rcs. The analysis of the data allows us to sustain that different forms of Rcs. coexist at a same age and that they distribute their contexts of usage and their discursive functions. These results do not coincide with those of obtained previously in experimental studies (Gili & Gaya, 1972; Múgica & Solana, 1999; Solana, 1996, 1997). We believe that this discrepancy is due to the methodological tool used because it allowed observing the interrelation between syntactic forms and others discursive competence factors, such as Media Length Utterance. In sum, the methodological resource proposed seems to be a valuable tool to preserve much of child language usage characteristics in context and to understand the complex dynamics of syntactic development. [ABSTRACT FROM AUTHOR]