Achievement test scores - unfortunately - don't help much with placement.
What about you son physically moving to olderkid classrooms for one or two of his classes?
What about asking for end-of-year tests to see how he would do on this year's, next year's and 'compact' the curriculum so he doesn't get unneeded repition.
What about better 'Folder Work' - you may have to supply it yourself, or get 'Folder Work' from teachers who teach older kids?
Is an online class allowed during the school day?
How is his keyboarding going?
Could you start a 'Jr. Great Books' literature discussion group with some of the brightest kids from his grade and the grade above?
Does he have a favorite topic that he could use as an independent study project instead of realms of 'Folder Work?'
Best Wishes,
Grinity