In this paper, we investigated the contribution of both cognitive and affective factors to mathematical skills. In particular, we looked at the protective role of self-concept for mathematical learning and performance. In a field study, we tested the relation of math self-concept and short-term visuo-spatial working memory to the mathematical abilities of second- grade primary school children in Italy (N = 105). Measures included the "Test for the evaluation of calculating and problem-solving abilities" (AC-MT 6-11), the backward Corsi blocks test (Battery for Visuo-Spatial Memory), and the mathematics self-concept sub-scale of the Self-Description Questionnaire-I (SDQ-I, Italian version). As expected, correlation and moderated regression analyses showed that mathematics self-concept and working memory both positively predict mathematical operations and numeracy, but not accuracy. Simple slope analysis confirmed our moderation hypothesis, with working memory predicting mathematical abilities at low levels of math self-concept, but not at medium and high levels. The theoretical and practical implications are discussed.