PLATO and TICCIT, two systems of computer-assisted instruction, are analyzed with a view to determining their educational effectiveness. This report presents an overview of how this will be accomplished, in full awareness that the concept of "effectiveness" has been subject to diverse interpretation. To avoid misunderstandings, the concept is given as much prior elaboration and specification as is now possible. The entire context of this evaluation of educational effectiveness will be clarified by the delineation of four essential issues; the what, who, how and when of the evaluation. Together these basic questions form dimensions of the analytical approach to evaluating the educational effectiveness of PLATO and TICCIT.