Thanks to Greg Olley for sending a copy of the following 2007 article from the University of Richmond Law Review.
Bonnie, R. J. & Gustafson, K. (2007). The challenges of implementing Atkins v Virginia: How legislatures and courts can promote accurate assessments and adjudications of mental retardation in death penalty cases. University of Richmond Law Review, 41 (4), 811-860. (Click here to view/download)