Which of the following is NOT a model that helps students understand subtraction?

The correct answer, "Adding Zero," is not a model that helps students understand subtraction because adding zero does not directly relate to the concept of subtraction itself. Subtraction involves the removal of value from a total, typically demonstrated through various other models that provide a clear understanding of what it means to take away, decrease, or differentiate quantities.

Counting backwards helps students grasp subtraction by visualizing the process of removing items from a set, while using number lines allows them to see the distance between numbers, reinforcing how one number is decreased to reach another. Taking away objects provides a tangible and visual representation of subtraction that allows students to see and manipulate quantities directly. In contrast, adding zero maintains the same value and does not correspond with the action of subtracting or reducing quantities.