Learning and teaching as well are processes reasonable control of which is supported by the information feedback. Knowledge assessment can be incorporated as a part of this self-control or control process. In this paper the possibility is studied how to formalize this assessment in the case when the measurement of the knowledge of the subject to consider is supported by the school-achievement test of the multiple-choice type. The relation between the actual subject’s knowledge and his/her response in the test is given by means of the binomial distribution and the assessment reliability is expressed by the set of operation characteristics. The possibility to apply entropy and distance of a frequency distribution as the means of the assessment efficiency evaluation is demostrated. Functioning of the method is proved in the cases of some multiple-choice tests of the size and number of distractors commonly used.