The ability to design experiments in an appropriate and efficient way is an important skill, but students typically have little opportunity to get experience. Most textbooks introduce standard general-purpose designs, and then proceed with the analysis of data already collected. In this paper we explore a tool for gaining design experience: computer based virtual experiments. These are software environments which mimic a real situation of interest, and invite the user to collect data to answer a research question. The following prototype environments will be described: an industrial process that must be optimized, a greenhouse experiment to compare the effect of different treatments on plant growth, and an arcade style applet that illustrates the use of t-tests, regression and analysis of variance. These environments are parts of a collection called env2exp, and can be freely used over the web. They have been used in several courses over the last two years.