In fish in a tree What is the significance of coins in this story? How are they meaningful to Ally and Travis?

Ally and Travis are siblings. They can't read because they both have dyslexia. However, they can do numbers and can count money very well that is why the coins are very important for them. The coins they have also hold a special meaning to them.

Travis bought 1933 mercury dime. He bought the coin because it was the year their Grandpa was born.

Ally also have a 1943 steel penny. She brought it to class to show it as a representation of herself. The coin was given to her by her father when he was being deployed.