When John thinks 'trade them one for one' he means that inorder for him to go to school, Audrey must stay home.
Step-by-step explanation:
John is a character in one of R.V. Cassill's story 'The First Day of School.' The story revolves around a boy John who have to go to school with his younger sister Audrey.
It was the first day of their school and that's when the segregation took place. And so John being concerned for the well being of her sister, tells her that she must stay home. He says this, so that he can go to school.