Theory-driven conceptualizations of phonological abilities in a sufficiently transparent language (Greek) were examined in children ages 5 years 8 months to 7 years 7 months, by comparing a set of a priori models. Specifically, the fit of 9 different models was evaluated, as defined by the Number of Factors (1 to 3; represented by rhymes, syllables, and phonemes) x Relationships Between the Latent Variables (orthogonal vs. oblique) x Level (first vs. second order). In addition, the invariant sequence of phonological abilities was examined through longitudinal factorial invariance. We administered a set of 10 phonological tasks that differed in linguistic complexity to 280 Greek-Cypriot children. Reading fluency was also assessed to externally validate the conceptualization of phonological sensitivity. The results provided evidence for the model that depicts phonological sensitivity as a unified construct that develops in an invariant structure across time and significantly predicts a child's reading performance. (Contains 3 figures, 4 tables, and 3 footnotes.)