This isn't specific to gifted students but it does adress growth on MAP testing.
We should also keep in mind that, even in the best schools, many children do not succeed in
achieving their growth index target. In the top 10% of schools about 60 to 70% of the students
reach their RIT point growth norm target in reading, while about 65 to 75% of students meet this
target in mathematics. When setting targets using this statistic, educators should remember that a
school in which more than 70% of the students meet or exceed their growth index norm is
exemplary.
http://illinoisnwea.wikispaces.com/file/view/SchoolGrowthNormStudy2006-Final.040407.pdf
