Cognitive flexibility fosters students to solve problems. Fostering cognitive flexibility is therefore a major stake in mathematics education. This research introduced a learning method to develop mathematical concepts when solving word arithmetic problems. The study was conducted with 8 classes (4th-5th Grades) from high-priority education schools in the Paris area following this protocol: pre-tests, 5 learning sessions for experimental and control groups, post-tests. During learning sessions, students studied arithmetic word problems that can be solved in two different ways: an expansion strategy and a factorization one. The experimental teaching method, based on a recategorization principle, allowed experimental students to improve more than the control students in ability to use the factorization strategy even in contexts where it is the less intuitive and to consider the two successful strategies . Educational entailments of our finding are discussed.