Newborn to 4 months old
- recognizes the difference between a picture with two dots and one with three dots
- shows surprise when a puppet jumps more times than they are used to seeing
5 – 6 months old
- recognizes the difference between a jar that is half full of juice and one that is full
- shows surprise seeing three toys when there are only supposed to be two toys
- identifies the difference between two large sets of toys if one of the sets is at least twice as large as the other (e.g. can see that a set of 12 toys is different from a set of 24 toys)
9 – 12 months old
- identifies the difference between two large sets of toys even if the sets are almost the same size (e.g. can see that a set of 8 toys is different from a set of 10 toys)
12 – 18 months old
- learns to pick the smaller of two sets of small blocks
2 – 3 years old
- learns some number words
- labels toys with number words
- knows that when one candy is taken away from two candies, one candy is left
- knows that when one candy is added to two candies, there are three candies altogether
- tries to count using number names but may not have them in the correct order
- says number words in the same order every time when counting objects, but they may not necessarily be in the correct order
- recites the number words from 1 to 10
- represents 1 and 2 using fingers
- divides up toys between two children by using a “one-for-me, one-for-you” strategy
- identifies the “first” and “last” person in a line