Virtualization tools, useful softwares that enables tests and evaluation of functionalities, have been used in computer network classes to provide an environment for practice experiments. Although some papers describe these tools and their technical benefits, they do not provide quantitative information about its effectiveness. This paper presents a proposal for systematic use of this category of tools in computer classes and a evaluation of the Netkit tool use in computer network classes. It will be shown how tutorial sections have been developed to these courses, the receptivity from the students through surveys and a statistical analysis of how much students grades can be improved by applying such tutorials. Finally, it will be possible to conclude that, in fact, the use of such tools is strongly advised.