Educational assessment is a part of accountability in K-12 education, and teachers often face ethical dilemmas in assessment practices. We conducted a comparative mixed-methods study of teachers' perspectives on educational assessment practices in the United States and China. A survey with 255 teachers based on 14 assessment scenarios within seven categories revealed that American teachers and Chinese teachers had consistent views on five scenarios, and they referenced common assessment guidelines in their justifications for whether they view certain practices as ethical or not. They disagreed on nine scenarios, prioritizing different guidelines to support their views about whether certain practices were ethical or not. Within each culture, teachers' views of certain scenarios differed based on gender, academic degree, years of experience, and grade levels taught in certain scenarios. The differences in teachers' views and reasoning were shaped by their cultural backgrounds, educational and professional experiences, and educational systems and policies. The findings can help raise educators' awareness of assessment practices shaped by cultural contexts, guide teaching, learning, and assessment, and inform educational policymaking and program development.