Research shows that students often master doubles combinations (like 2 + 2 = 4, 3 + 3 = 6, etc.) more easily than most other math facts (National Research Council, 2001). This makes doubles a key foundational skill, especially since harder facts (like 7 + 8) are often close to doubles.
While even here, we move from concrete to intermediate to abstract levels, here’s how an abstract level of working with doubles can look like.
