The Robin Hood Effect of NCLB?

Sam Dillon, writer for the New York Times, writes the following in Wednesday's New York Times, June 18, 2008
" A new study argues that the nation's focus on helping students who are furtherest behind may have provided a Robin Hood Effect, yielding steady academic gain for low achieving students in recent years at the expense of top students"
What? One wonders why the research dots are connected so that the above conclusion might be reached?
On one level, lets take the high schools. Top students tend to have highly qualified teachers. These teachers meet the standards in some cases for teaching advanced placement classes. Such teachers, because of their qualifications, may not maintain a teaching schedule that includes academically underachieving students.
On another level, lets look at lesson planning. Are we saying that classroom teachers do no planning for any students but the low achieving? Thus, the improvement in scores for that demographic? Really? My reality is such that the high achieving student requires the most extensive planning to address the depth of curriculum content that their intellect and cumulative knowledge requires.
Hmmmmmm-more to come on this topic