At my kids' school they have several tables in the foyer which are completely covered with lost and found lunch boxes, backpacks, jackets, t-shirts, books and more. These tables stay full, sometimes piled to overflowing! They remind parents and children to look through these items several times a year to see if it belongs to their child. Still, we donate what is left over every year to charity. I suspect that most of these items are found in the lunchroom, halls, gym and in the area outside where kids wait for busses and parents to pick them up.
Maybe items which are left in their own classrooms are more likely to be returned to the proper owner, but I am surprized to read the experiences of teachers here at WS who have never had a child leave personal items in their classroom. I guess it depends upon the size of the classes and dilligence of the teacher.