North Carolina Standard Course of Study
NC.1.NBT. Number and Operations in Base Ten
Understand place value.
NC.1.NBT.2. Understand that the two digits of a two-digit number represent amounts of tens and ones.
NC.1.NBT.2.a. Unitize by making a ten from a collection of ten ones.
NC.1.NBT.2.b. Model the numbers from 11 to 19 as composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
NC.1.NBT.2.c. Demonstrate that the numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens, with 0 ones.