Reading Recovery is an early literacy intervention designed for first grade students who are considered at-risk of failure in learning to read and write after one year of formal schooling. This study has three main objectives based on the series of scores obtained from the administration of the Observation Survey within a school year. The first one aims to evaluate the effectiveness of Reading Recovery. The second objective considers the time of the year when the intervention occurs. The third objective consists in determining the predictive value of the reading and writing measures used in this program. A total of 1044 children at-risk of early reading difficulties were identified upon entry in grade one and received one-to-one daily thirty minute lessons offered by qualified Reading Recovery teachers. An Observation Survey of early literacy achievement (Clay, 2002) was used to assess emergent literacy in children during two separate period during the school year: at the time of Entry or pre-test and at the Exit or post-test. Data were also available for over 300 successful Reading Recovery students who were re-assessed at the end of the school year. These data were analyzed to establish the long-term effect of the intervention within the same school year. Findings suggest that the early intervention is effective for nearly 80% of low performing first graders to reach the average range of their peers in terms of literacy achievement on all measures. The successful children who had benefited from Reading Recovery early in the school year had reached the average range by the time the next group of children had been selected. Amongst the measures comprised in the assessment materials Letter Identification and Hearing and Recording Sounds in Words were the best predictors of success.