The purpose of this research was to assess the development of phonological skills before and during learning to read. Thirty-four children were tested twice, in nursery school and in first grade with an epiphonological task (E), e.g. judgment of similarity, and two metaphonological tasks, one requiring the extraction of common units (M1) and one requiring unit substitution (M2). As expected, performances decreased from E, to M1, to M2. In response to formal instruction, phonemes yielded better performances than larger units, particularly in M1. The correlations between scores in written word recognition test and phonological skills confirm the strong link between phonemic awareness and learning to read. However, syllable seems to be an important unit in phonological processing. The results are discussed in terms of the cognitive load involved in the different tasks. A List of experimental trials in the phonological tasks is appended. (Contains 5 tables and 4 notes.)