Based on a theory of situated learning, assessment must emphasize process as much as product. Assessment must move away from a linear additive model, accepting at the outset the complex, nonlinear, and possibly chaotic nature of real learning. Assessment must adapt to and take advantage of students working with technologies that extend their perceptual and problem-solving capacities beyond what they could do alone. To illustrate these points, several assessment examples are given, including a computer-based planning assistant for a videodisc mathematics and science video, suggestions for computer-based portfolio assessment, and speculations about embedded assessment of virtual situations. In all cases, the theory of situated learning emphasized perception over memory and the codetermined nature of learning and thinking.