The acquisition of reading skill was studied in 503 Italian children in first to eighth grade using a task that required reading of lists of words and non-words. Analysis of the metric characteristics of the measures indicated that reading speed but not accuracy was normally distributed across all ages considered. The role of specific effects (length, word frequency, and lexicality) versus global factors in reading speed was examined using the Rate-Amount Model (RAM). A global processing factor accounted for a large portion of the variance. Specific influences of length, frequency, and lexicality were detected in different periods of development over and above the global processing factor. Length modulated performance at early stages of learning and progressively less later on; in the case of non-words, the effect of length was large but did not change as a function of grade. The "lexicality" effect, present at all ages for high frequency words and by third grade for low frequency words increased with reading practice indicating a progressive differentiation in the ability to read words and non-words. Finally, the effect of word frequency was highest in third grade and then decreased. These findings are discussed in terms of their relevance for reading acquisition in a language with transparent orthography and their implications for evaluating developmental reading deficits. Overall, it is proposed that RAM is a useful tool for disentangling the role of specific versus global factors in reading development.