If we are intent on ensuring that all children make educational progress, and we are intent on being able to measure that progress through testing, it seems to me that, rather than having a single (low) passing score which all children must meet, which pretty much dooms the high-achieving kids to educational neglect, the rational way to approach this would be to track individual scores on meaningful measures yearly, and mandate that the schools ensure that all children who are performing at or above grade level at the beginning of the school year make at least one year's worth of progress from that point by the beginning of the next school year, and that children who are performing below grade level move closer to grade-level performance.
This would mean that low-performing students would need to make more than a year's worth of progress in a year, which might mean that districts would actually have to (gasp!) start providing services and intensive instruction to the kids that they identify as having learning disabilities. It might also mean that teachers would not be able to just ignore kids who had already mastered all the grade level content, but I for one, am willing to take that risk. They would have to provide appropriate subject acceleration or risk not meting their targets.
People value what gets measured and what gets praised or punished. If you don't measure and you don't reward appropriate education for gifted learners, you can't expect to see much of it happening in the schools.
