Parents' involvement with their children's schools usually starts as soon as they enter primary school. Parent Teacher Associations (PTAs) or Home School Associations (HSAs) welcome the fresh energy of eager new parents at the beginning of a long primary school life. But nursery school heads are not usually approached, so when I suggested starting a parents' group to Mary Hart, head of my son's Margaret McMillan Nursery School, it's no surprise she was a bit sceptical about how successful...