This paper proposes a reconsideration of use of computer simulations in science education. We discuss three studies of the use of science simulations for undergraduate distance learning students. The first one, "The Driven Pendulum" simulation is a computer-based experiment on the behaviour of a pendulum. The second simulation, "Evolve" is concerned with natural selection in a hypothetical species of a flowering plant. The third simulation, "The Double Slit Experiment" deals with electron diffraction and students are provided with an experimental setup to investigate electron diffraction for double and single slit arrangements. We evaluated each simulation, with 30 students each for "The Driven Pendulum" and "Evolve" simulations and about 100 students for "The Double Slit Experiment." From these evaluations we have developed a set of the features for the effective use of simulations in distance learning. The features include student support, multiple representations and tailorability.