I agree with this 100%!
Let me share my experience. I started Kinder early. I skipped 3rd grade. I started high school at 12 years old. I didn't belong there. I could do the work (and faster/better then the 14-15 year olds) but I was NOT ready emotionally or socially. I started college at 16. I didn't belong there. Don't get me wrong, I had TONS of friends, was a cheerleader, student council member and actively participated in social activities, but I was also exposed to stuff that no 12 year old should be- and no matter how happy and well adjusted on the outside, I was a mess on the inside and very angry. I am 37 now and it took a long time for me to come to terms with my parents for their decision to fight the school and force them to skip me.
I was smart enough, but I was not mature enough. I missed some really important social lessons during the time that they were so focused on me "not being bored" or "needing more challenges" etc. All those things that parents say to push their kids harder. I had days where I was bored but I also had days where teachers took the extra time to engage me in activities that were more challenging in class, yet allowed me to still interact with peers- that was BEFORE my parents made such a big deal out of me being smart.
My own four kids are all GATE students. They could easily do the classwork of a grade or two higher then where they are, but I don't think that is where they belong.They were all reading at the 5th grade level by first grade, all but the oldest were self taught. For me, it is more important that my kids are well adjusted socially and HAPPY. I would NEVER request that my kids be skipped. In the real world, being socially adept is much more of a predictor of success and happiness than intelligence. Do some reasearch, there is a ton of information regarding EQ or emotional intelligence.
I work together with my kids teachers to give them challenges in class. If it means I have to go to the school and make copies for the overworked teacher or research activities for them to do once they complete their classwork, then I do it. My kids' teachers have been great about keeping them busy and engaged, but it takes a dedicated parent who is willing to work WITH the teacher, not tell the teacher how to do his/her job.
My oldest is in middle school, the playing field is evening out for her. She is no longer the smartest kid in every class, especially in math. She actually has to work for her A's now. what's worse, she is learning life's lessons about mean girls and hormones!

I KNOW how much harder it would be for her if I had pushed for her to be a grade older and going through this.