Abstract
This paper contributes to determine student’s knowledge involved in arithmetic word problem solving, that are ignored by mathematics education research but discriminate reinvestment problems solving students: among these skills the use of a modeling approach (models are the arithmetic operations), different types of controls and the qualification. This paper shows how rich is a clinical approach after the solving session to discover ignored knowledge and feeds current (study of semiotic tools) and upcoming researches (controls and qualification) in relation to flexibility.