This paper describes an expert system based interactive "surrogate instructor" for use in acquisition of perceptual training motor and cognitive skills related specifically to rifle marksmanship tasks. The objective of the surrogate instructor is to provide computer-based trainee task intervention just as human instructor provides when "looking over the shoulder" of the trainee. The instructional function will be provided by an expert program that will perform consistent diagnosis and individualized instruction while emulating either a specific instructor or an ideal human instructor. The system architecture is based on a real time blackboard model based on the "cooperating expert paradigm": These are (a) The Task Expert Model which makes up the standards of performance; (b) The Trainee model which tracks performance behavior and represents evolving trainee knowledge and skill; (c) Instructional model, which performs rule-based diagnosis of the trainee with respect to the expert model and generates instructional feedback; (d) A Curriculum Library which contains the instructional knowledge elements. The knowledge representation formalism central to the development of the expert model is the modified Petri Net (MPN). This model provides the procedural skills representation for training of psycho-motor skills. The (MPN) representation performs a two-fold function: (1) it provides the mechanism for robust representation of trainee behavior/performance for training diagnosis and (2) provides the basis for comparing a descriptive trainee behavior/performance model against an expert prescriptive performance model.