Mark was fascinated by Amanda – 'She was so smart' – and followed her home from school to discover her smoking in the woods behind her house. She met Amanda’s mother, who agreed to let her come back at the weekend to take more pictures. Amanda was excited about the shoot and put on makeup for the event. At the end of the day, Mark went out to the back garden to say goodbye, and it was there that she found Amanda, 'fake nails and everything', posing in the paddling pool with her cousin, smoking a cigarette. 'That’s what I love about documentary photography,' Mark says. 'There are so many incredible surprises.' Photograph: Mary Ellen Mark