An important aim of education is that students learn to think critically about moral values. This study examines how five secondary school philosophy teachers implement and evaluate design principles for promoting value-loaded critical thinking in whole-class dialogues. The five design principles are: address, apply and reason critically about moral values, create intercontextuality, and promote metacognitive reflection. For our evaluation, we first analyzed teachers’ judgments of the relevance, consistency, and practicality of the design principles. Secondly, we conducted classroom observations to analyse teachers’ implementation of the design principles. We find that teachers consider the design principles relevant, consistent and mostly practical and that they use a wider range of teaching strategies for each design principle, after participating in this study.