Purpose: The slogan "Practice what you preach" denotes that people should behave in accordance with the values that they preach. For universities that teach sustainable development (SD), it implies that these institutes should apply major SD principles themselves for example by campus greening, green purchasing, etc. But is not "Practice what you preach" a questionable slogan in that regard that university teachers should not preach values, i.e. transfer values to their students by the authority of their position? Which value statements are acceptable and which are not? Design/methodology/approach: The paper presents the results of a survey among international SD teachers in engineering on the acceptability of value laden statements. Moreover, the paper presents results regarding the values that SD teachers represent, and compares these results to survey results among engineers and engineering students. Findings: SD teachers in engineering are more critical about the role of technology in SD than their students and professional engineers are. However, there does not seem to be a real gap between students and teachers. Practical implications: It is argued that academic education on SD should aim at clarifying moral issues and helping students to develop their own moral positions given the values that are present in the professionals' work. Teachers' options how to address moral issues without preaching are briefly described. Originality/value: This paper strongly argues against preaching. (Contains 3 tables, 1 figure and 2 notes.)