I know for my DS6, six was the age of boredom. At four, being at kindy was all play (although they were great, and could see he was way ahead so they got him to write up signs and read to the class, etc), so my son was looking forward to starting Reception (the equivalent to US' kindy). It was hardly challenging, but my son enjoyed the social aspect. Now, at six and in year 1, he is getting very bored. He is doing year two maths, but it's not enough. I'm glad that, where his teacher was once against a grade skip, she now supports it.
So he will be doing year 3 next year. Thank goodness! I know that my son would REALLY hate school if he didn't skip. My son used to say on the start of the weekend, "I wish it was Monday so I can go to school"; now he looks forward to the weekend so we can do our own learning.