Program visualization (PV) is potentially a useful method for teaching programming basics to novice programmers. However, there are very few studies on the effects of PV. We have developed a PV tool called ViLLE at the University of Turku. In this paper, multiple studies on the effects of the tool are presented. In addition, new qualitative data about students' feedback of using the tool is presented. Both, the results of our studies and the feedback indicate that ViLLE can be used effectively in teaching basic programming concepts to novice programmers.