This study was designed to examine the developmental course of the suffix frequency effect and its role in the development of automatic morpho-lexical access. In Spanish, a highly transparent language from an orthographic point of view, this effect has been shown to be facilitative in adults, but the evidence with children is still inconclusive. A total of 90 2nd, 4th and 6th grade children performed a go/no go lexical decision task, with words containing either high or low frequency suffixes. Results showed significant main effects for grade and for derivative suffix frequency, with no interaction between both. This finding suggests that the suffix frequency effect emerges very early in reading development and that its role is well established from the beginning of reading experience, suggesting that sensitivity to suffix frequency can be a good predictor of a child's ability to internalize orthographic regularities at an early stage. These findings are interpreted in the light of previous evidence paying special attention to orthographic transparency and morpheme regularity in Spanish language.