Which tier involves adding onto the larger number, as well as decomposing single digit numbers?

The first tier typically focuses on foundational concepts in mathematics, which includes essential skills such as basic addition and decomposing single digit numbers. In this tier, students learn to work with numbers by building upon larger numbers, grasping the concept of numbers in a more comprehensive way, and understanding how smaller components can make up these numbers. By breaking down single-digit numbers and adding them effectively to larger quantities, students become equipped with the necessary tools to tackle more complex mathematical problems in the future. This foundational knowledge is critical for building a solid understanding of arithmetic.

Other tiers often introduce more advanced concepts or different types of mathematical operations that go beyond the simple addition and decomposition of numbers that are emphasized in the first tier. Therefore, the first tier being the correct choice highlights its primary role in establishing these basic mathematical competencies.