Through increased understanding of both psychology and the brain, we now know that individuals learn best when they are in a context that provides a moderate challenge.
Searching for the perfectly moderate challenge is the quest of the differentiating teacher. Will the assignment be so hard that frustration overwhelms the student? Will the assignment be so easy that boredom seeps in? Here's how Tomlinson says it:
Put another way, students who consistently fail lose thier motivation to learn. Students who succeed too easily also lose their motivation to learn.
She also challenges teachers to never give up on any student:
It is unacceptable for any teacher to respond to any group of children (or any individual child) as though the children were inappropriate, inconvenient, beyond hope, or not in need of focused attention.
We all would benefit from checking our assumptions at the door. I know I've been guilty of giving up on students. Let's hold each other accountable to find a way to reach every child.