California had a grade-school program in the 1970s called MGM - "Mentally Gifted Minors" - which focused on the top 2% (IQ 132+). It was cool, but IIRC at my school it basically replaced a single class period per week - I think it was taught by one part-time teacher who rotated between different schools on different days, trying to keep kids intellectually engaged and relieve them from the most tedious stuff they would otherwise have to suffer through.

These new tools (or Khan Academy, or even the self-paced books that homeschoolers used to use) would probably allow kids to make a lot more progress were they so inclined.