My 6 year old grandson just got a stripe TAKEN OFF HIS BELT by his instructor because apparently wasn't paying attention. In front of the whole class. Is this appropriate in BJJ?
don't see why not. the stripes are really there to keep the kids interested and motivated.
his might motivate him to pay attention in class in future...
Well, this is not something about in BJJ, this is not appropriate and unethical for a teacher to his student. He is only 6 years old, He had to work hard and his instructor need to pay him full attention. You also helped your grandson in training.
Without knowing the whole situation, it is difficult to draw any conclusions. But if after that your grandson became more attentive and the stripe was returned to him, then it means the instructor took it away for a reason