The study reported in this paper is an attempt to develop a comprehensive model of measuring problem solving and posing (PSP) skills based on Marshall's schema theory (ST). A battery of tests on PSP skills was administered to 5th and 6th grade Cypriot students (n=2519). The Rasch model was used and a scale was created for the battery of tests and analyzed for reliability, fit to the model, meaning and validity. The analysis revealed that the battery of tests has satisfactory psychometric properties. The identified scale verifies previous findings suggesting that a number of variables are interwoven in the problem solving process. Yet, problem representation possesses a critical role in the process. The scale also suggests that achievement in posing problems is affected by the type of given information. The findings are discussed with reference to intended uses of teaching mathematics and suggestions for further research are drawn. (Contains 1 figure and 2 tables.) [For complete proceedings, see ED500859.]