Generalizability is a particularly adequate statistical model when it comes to refining devices for the evaluation of learning. It allows one to verify whether an evaluation instrument possesses the necessary psychometric properties to place learners’ results on a given scale, that is to say with respect to a previously defined criterion. To illustrate it, we have chosen the example of a physics test on the subject of heat, given at the beginning and the end of a series of laboratory courses. We present examples of the possibilities of the model for dealing with some of the problems that can arise in a didactical sequence.