Absolute nonsense. When you find a good student struggling, give them extra credit work and help them to catch up. They will learn many life lessons in the process.
Funny story—I went to a fancy prep school.
I was terrible at foreign languages—just awful.
They made me take one and I heard through the grapevine that French was the easiest to learn.
So I took French.
The teacher got totally frustrated with me and finally one day blurted out my name and said “you are awful at this. You will never learn this language.”
I was totally humiliated.
I hated French so much that I studied hard enough to pass the Advanced Placement exam so I didn’t have to take it in college.
:-)