The aim of this study was to explore principals’ perceptions of school practices that have ethical meaning through a transnational perspective based on the 8th grade TIMSS 2015 international assessment. The sample comprised 8353 principals from 8353 different schools and 280,130 students that participated in the TIMSS 2015 survey. We used principals’ ranking procedure and Mplus for exploratory and confirmatory analyses, multilevel confirmatory analysis, and multiple group comparison. The results indicated that principals’ perceptions include three main dimensions with an ethical meaning: ‘caring for students’ learning’, ‘respecting the rules amongst students and teachers’ and ‘parents’ and students’ involvement in schooling’. These dimensions broaden the meaning of existing dimensions describing ethical practices in school leadership. In addition, they were found to positively predict students’ science achievements. The novelty of this study is reflected by the results, leading to the understanding that the TIMSS principals’ questionnaire has an additional meaning, which goes beyond its original parameters. The findings may lead to a better understanding of the importance of the role of educational leaders in promoting ethical school practices. This study set out to elicit a new transnational measure, which may warrant an exploration of the similarities and differences between countries.