Summary : Procedural resolution or direct retrieval in memory of simple addition and multiplication in children ? The present experiment aimed at studying the resolution of simple additions and multiplications in fifth-graders. The operations were those including two digits (2 to 9), except ties. The task was operation verification. The results showed that the operands' size effect and the priming effect ofthe sign were greater for addition than for multiplication. The results suggested that multiplication is solved by a direct retrieval of the answer from memory, whereas addition is solved by an algorithmic strategy. These results replicate those found by Roussel, Fayol and Barrouillet (2001) in adults, and are discussed in the scope of the ACT-R model (Anderson, 1993). Finally, this study suggested that, except for an increase of speed, the nature of the strategies used to solve simple additions and multiplications does not change with development. Key words : cognitive arithmetic, strategies, cognitive development, size effect, priming effect, interference effect.