An established literature draws on ecological concepts to analyze interrelationships within education structures and processes, and the impact of shifting balances. Private supplementary tutoring--relatively new in ecosystems of education around the world--is creating significant changes in relationships, particularly as they concern teachers' roles. This paper, drawing on data from Hong Kong, where private tutoring has become very visible, presents perspectives on the phenomenon from students and teachers. It shows that these parties sometimes play complementary roles, but that private tutoring may marginalize teachers in some respects. Insights from these perspectives suggest a research agenda for other parts of the world as well as for Hong Kong.