The impact of computer-based communication on group performance depends upon the structure enforced by the communication system. While the ability to introduce structures which enhance human communication processes has been applauded, research to evaluate the impact of various design features is lacking. This research has explored the impact of two synchronous systems which vary in the role of immediacy of interaction and feedback on group decision making. One system is message-oriented, requiring a conferee to complete a message before interacting with others. The other displays what each group member is typing in a separate window on the screens of all participants. In this system, comments can be made as ideas are expressed. Groups were asked to solve a problem first individually and then cooperatively using one of the two systems. All groups produced decisions superior to the average initial individual solutions. Window system groups both improved more and produced significantly higher quality decisions. These groups focused on fewer topics at one time while spending less time discussing how to organize both system and task efforts. By influencing the group's ability to organize and focus its attention, the design of the communication system influenced decision quality.