Abstract: The aim of the present study was the design and evaluation of a computer-supported collaborative learning environment in which upper primary school children are guided and supported in becoming more strategic, motivated, communicative, mindful, and self-regulated mathematical problem solvers and problem posers. Major characteristics of the learning environment were: use of a varied set of challenging word problems; application of highly interactive instructional techniques supported by ‘Knowledge Forum’ (a cognitive, technological tool for knowledge construction and exchange); creation of a fundamentally new classroom culture and climate. Major results of the study are: the participating teachers implemented the learning environment appropriately; the learning environment was received enthusiastically by the pupils; the intervention had a significant positive effect on sixth graders’ problem-solving competency.