Several initiatives have been implemented worldwide to foster student interest towards STEM disciplines. These initiatives are based on the awareness that mathematics is essential for scientific and technological advancement: it trains to reasoning and reflection, stimulates logical capabilities and intuition, improve investigation attitude. Most of them recognize also that mathematical problem solving represents an effective way to support teachers and students in their teaching and learning activities, respectively. In this context, this work is aimed at presenting OPS4Math (Optimization and Problem Solving for Teaching of Mathematics), a training project for Secondary School teachers, supported by Italian Ministry of University and Research. The driving idea, widely discussed by the scientific community, is to operate a reversal of the didactical perspective: starting from phenomena/problems to introduce concepts of data, variables, relationships and functions in an appealing way. We present project organization, structure and aims, to give useful hints for its replication.