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This paper assesses the effects of the ACE (Arithmétique et Compréhension à l’École élémentaire) teaching program implemented in 58 experimental classes at first grade level (priority and regular education) for teaching arithmetic. The results of the assessment at the beginning and the end of the school year show a stronger improvement in the experimental classes than in the 49 control classes. They also show that this improvement is significantly higher in priority classes than in regular classes. These effects do not appear to be reducible to methodological artifacts (Hawthorne effect, type of assessment items, mode of response) and allow us to consider the generalization and the transfer of the essential elements of this mathematic curriculum to higher grades.