The Common Core math standards suggest that first graders "think of whole numbers between 10 and 100 in terms of tens and ones" and solve problems such as "6 + 7" by "creating equivalent but easier or known sums" like this: "6 + 6 + 1 = 12 + 1 = 13." For other facts about Common Core math and videos of an educator teaching it, see the documentation link below.