On the Atrai River in the northwest of Bangladesh, a small beige boat is tied up in tall grass that lines the riverbank.
The interior of the boat is packed with narrow benches which in turn are jammed with children.
There are 29 students in this third-grade class and it would be hard to fit any more into the narrow vessel. The kids sit shoulder-to-shoulder facing a blackboard at the back of the boat.
When the teacher asks for a volunteer to recite a multiplication table, 8-year-old Nila Khatun's hand shoots straight toward the unpainted ceiling.