One-to-one correspondence is fundamental to counting. When we count out a deck of cards, we say, 1, 2, 3, ... , 52, and as we say each number we lay down a card. Each number corresponds to a card.Before learning to count a child needs to understand 'one to one correspondence'. This is being able to match one object to one other object or person. Children practice this skill any time they pass one item out to each person, or match items up.