The thesis of this paper is that legacy and approach of the Polish Praxiological School determine promising material to develop praxiology as metatheory for management sciences. The idea of developing praxiology as metatheory for management sciences is advanced and long-term research project (in text the author groups its problems in seven, correlated areas). Comparative analyses of subject literature allows the author to submit a proposition that, basic theorems of praxiology, i.e. practical directives (both as logical and normative sentences) are similar in many ways to organization theory theorems. Therefore, he thinks, that with help of certain theoretical interventions, one can use (and develop) praxiology and metapraxiology to work out some of the management sciences metatheoretical problems. These problems are, e.g. structural chaos and ambiguity of basic management sciences terminology. The author focuses his attention on: 1) designing of praxiological systematization of management sciences, and 2) application of idea of praxiological efficaciousness to solving the ambiguity problem of basic management sciences terminology (shown on the example of effectiveness term).