How is your older son going now Kai? In many ways you could have been talking about my older son - the school seems happyy that he is performing average (consisting of marks that range from the bottom through to the very top and that is only one subject!!). My two have similar intelligence - but boy do they 'display'at school differently. To other people, it almost seems that the younger 'got it all' and the older missed out.
We pulled him out of school at the end of first grade and have been homeschooling now for six years. He's doing really well now. This past year he started on meds for the ADHD and I finally got him standardized testing accommodations through the school district (504) that he used for the first time this spring. The difference was amazing: 99th %iles down the line (except for spelling!). He will be officially starting high school (a year ahead, and two years ahead if I had let the school have their way) in our homeschool next year, though he has been doing some high school level work for the past three years.
It's working out here. It has been a long haul. I am certain that if he had stayed in school that we would be having a different experience right now.