Developmental Milestones
Written by: Helena P. Osana and Diana A. Royea, Concordia University
Age 
Attributes 
0 – 12 Months 
Thinks about numbers in simple ways. Sees whether two small quantities are the same or different. Sees whether moving quantities are the same or different. Can immediately see “twoness” and “threeness.” Sees that two large sets of objects are the same or different provided that one set is twice as large as the other set, and later (between 9 and 12 months) can tell if two large sets are the same or different even if the sets are closer in size. Realizes something is wrong if one object is added to another object and the wrong number of objects results. Sees the difference in continuous quantities, such as different amounts of juice in two different containers. 
13 – 36 Months

Can tell which of two sets of quantities “looks like” it contains more. By two years of age, shows an emerging awareness of the effects of adding a small quantity to or taking a small quantity away from a group of objects. Learns first number words. Labels toys with number words. Number words are consistently used in the same order even though the sequence may not be correct. Can learn to point to objects only once when counting a group of objects. With practice, can learn to correctly recite the number words from 1 to 10 in the correct sequence. Can name the next number word for numbers below 10 if allowed a running start, that is counting from one each time Shows a continual improvement in counting skill throughout this period. 
37 – 48 Months

Begins to understand that numbers can represent quantity or “how many.” Learns that numbers that come later in the counting sequence are larger than the numbers that come before. Can represent numbers up to 5 using finger patterns. Can name the next number word without a running start. Many can count to 20, 30, or higher. Can learn to count backwards from 5. Basic knowledge of arithmetic gets refined; some children can give the correct answer to small number addition and subtraction problems (provided the problems are presented nonverbally with manipulatives). Equally distributes up to 10 items between two people using a “one for me, one for you” strategy. After having equally distributed a collection of items, knows how many is in each share by counting the number of items in one share only. Understanding of continuous quantities that cannot be counted improves (e.g., knows that when sand is added to a pile of sand, the pile gets bigger). Uses vocabulary such as “taller,” “shorter,” “fatter,” “skinnier,” “wider,” and “longer” when talking about comparing objects. Nearing fourth birthday, many can recognize the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9. 
49 – 60 Months

Can learn to count up to 100.
Starts counting forward from numbers other than 1. Counts backwards first from 5 and then from 10. By their sixth birthday, many can count backwards from 20. Can learn to skip count by 10s. Counting accuracy improves steadily during this period: At four years of age, can count 9 objects without making errors. At five years of age, can count 20 objects accurately. At six years of age, can count 28 objects (or more) without making mistakes. Uses pattern recognition to count more efficiently. Can learn to combine basic arithmetic skills and pattern recognition to count the number of items in a collection. Represents the numbers up to 10 using finger patterns. Can read onedigit numerals. First learns to write teens and by 6 years of age, can learn to write all the two digit numerals. Can identify written onedigit number words (“one,” “two,” etc.) and knows their corresponding numerals and cardinal values. Understands that a number is a counting word and at the same time corresponds to a cardinal value. Knows that it does not matter where you start counting when counting a set of objects and that number words do not adhere to the specific objects counted. By kindergarten, many can solve smallnumber multiplication and division problems if given physical materials to “act out” the problem. Understands that a group of 10 popsicle sticks is the same as 10 individual popsicle sticks, and later in this period, that a bundle of 18 popsicle sticks is the same as a bundle of 10 popsicle sticks plus 8 individual popsicle sticks. Recognizes “one half” and can learn to correctly label halves using the term “one half.” Develops quicker and more abstract methods for solving addition and subtraction problems. Can learn the doubles facts to ten. Reasoning about length, weight, and volume becomes more sophisticated. Can use objects, such as a piece of string, to measure the length of objects. Can make reasonable deductions about the lengths of objects. For example, if a book is shorter than the string, and the string is shorter than the plant, then the book is shorter than the plant, too. Can learn to use nonstandard items as units to measure the length of objects (e.g., laying paperclips end to end to measure the length of a book). Closer to the age of 6, can learn to use more conventional units, such as centimeters or meters. 