Even though feedback is an essential part of computer-based learning environments (CBLEs), it is still not clear what effect different types of feedback have on students math achievement and on their abilities to assess their own achievement. To approach this problem we are currently planning a quasi-experimental study with grade eight or nine students using a CBLE called “Discover Quadratic Functions”. This paper gives insight both into existing research concerning the design of CBLE as well as concerning different types of feedback and into the theoretical principals that guided the CBLE design. Additionally, results of a qualitative pilot study as well as the design of the up-coming main study are presented.