The Internet has been recognised not only as a tool for communication in the 21st century but also as an environment for enabling changes in the paradigm of teaching and learning. This paper describes our research effort on the design and delivery of quality educational material on object-oriented (O-O) testing in an Internet environment. O-O software testing has the advantage of being easily visualizable in terms of state changes and data-flows. We have attempted to show the inner workings of the complex processes involved in O-O testing. The O-O testing case studies considered contain visual images, animation, and interactive lessons, to assist active participation by learners to result in better understanding and knowledge retention. The distributed teaching and learning approach discussed in this paper employs appropriate UML diagrams, makes the diagrams test ready by including details of constraints as part of state/event transitions, and provides interactive lessons for learning O-O software testing. Furthermore, this paper describes a development process in visualization and interactivity to achieve improved learning outcomes of O-O software testing in an Internet based environment - (see http://www.sd.monash.edu.au/~sitar/se_educ_proj).