Bueller?� Bueller?� Bueller?

Maybe I didn't do a good job explaining or relating this to gifted children, so I'll try again. Test results based on grade level state standards don't seem to provide much information for parents of gifted children. MAP allows for growth assessment which can be much more informative.
Would comparing growth that a child shows in school to the growth that child shows outside of school (positive or negative) provide better school accountability than the current system?
I thought of a couple possible cons:
1) Some bad teachers could encourage children not to learn over the summer so the scores will look better. (probably over pessimistic)
2) For children that attend year round school, the time period that children are out of school may not be long enough for comparison.