"The Exception to the Rule" by it's very nature is not the normal or the average but the exceptional. That one who stands out.
I see it every day and I've watched myself defend it for years but only recently has it drawn my attension so much.
Children aren't so bothered by it but parents are generally irritated. They walk into a class, grading or tournament and spot the 10 year old brown belt. They haven't seen the 100 ten year olds who are below this level (the norm or the rule), just him and after letting their competitive irritation stew will at some stage over the next week approach the Sensei either directly "Why isn't Johnny that level?" Or indirectly to others within the club " If Johnny was in that dojo he'd be a black belt by now".
It's difficult as a Sensei to let the opinions of others pass by and hope that in time parents will see you have a plan to bring their child along at the best pace for their development and continued success. We as instructors want the very best for every student. Sometimes this is pursuing the next belt, the next tournament , an individual goal. But often it's about establishing confidence with where they are at right now. Growing into that yellow (or whatever coloured) belt, knowing which kata is which and bring able to help out beginners with the knowledge they have aquired.
None of us want to see our students disappointed and not reaching their potential .
Give your Sensei the benefit of the doubt, trust that after doing this a long time that they know what they are at.
