Critical analysis is universally advocated as a key goal of science teaching. In that context, the article explores the responses of beginning teachers (BTs) to explanations used in science education. Specifically, the study asks how BTs can be helped to ground their pedagogical choices in a critical analysis of explanations introduced during ordinary physics teaching. Referring to results from previous investigations, the main obstacles to activation of a critical attitude (even among experts) are discussed. On that basis, a tool is described for multi-criteria 'quality diagnosis' of such explanations. The two dimensions of this analytical grid are flaws (reasons for rejecting or having strong doubts about an explanatory text) and factors that may prompt misleading interpretations. Supplemented by more positive criteria such as simplicity or mnemonic value, three examples illustrate how the grid can be used to articulate the strengths and weaknesses of an explanatory text. In particular, the examples show how two explanations of the same phenomenon (in this case, flotation) can be compared using this form of multi-criteria analysis. The final section recapitulates the benefits and limitations of the tool and discusses more broadly how critical analysis can be supported and enhanced in the context of physics education.