Greater than and less than (> and <) are understood much more easily with the number line than the reform models. It's crystal clear. Several mathematical concepts – infinity, zero, negatives, infinity, fractions, decimals – are more easily accessible with the number line than with other models.

The number line doesn't ask English language learners, younger children who are just learning to read, and children who have other issues with reading and/or writing to deal with language-heavy models.

The number line doesn't present children with confusing story complications. The mathematical concept is the emphasis, and it doesn't get lost in the flood.

With the number line, the concept of "greater than and less than" doesn't get confused with "up and down" or "better or worse."

The number line is part of an incremental approach to learning mathematics, which appeals to children. They learn this step, then they learn the next step, then they learn the next one. But many reform approaches ask children to make huge leaps in understanding, while not giving them the basic skills they would need for those leaps.

The number line is easily dealt with on an individual basis, giving each student individual proficiency. But with reform approaches, an overemphasis on group work doesn't tend to lead to individual proficiency for children who learn to defer to others and to depend on others for answers.

In addition, the group work in some models (such as in the Postman Model) can be difficult for children who aren't as outgoing as others, and it can be excruciating for shy or autistic children.