I searched for the National Association for School Psychologists to get some info...but I don't know how to post links.
Here's some quotes pasted from the site...
"Impact at the elementary school level:
. While delayed entry and readiness classes may not hurt children in the short run, there is no evidence of a positive effect on either long-term school achievement or adjustment. Furthermore, by adolescence, these early retention practices are predictive of numerous health and emotional risk factors, and associated deleterious outcomes.
. Initial achievement gains may occur during the year the student is retained. However, the consistent trend across many research studies is that achievement gains decline within 2-3 years of retention, such that retained children either do no better or perform more poorly than similar groups of promoted children. This is true whether children are compared to same-grade peers or comparable students who were promoted.
Retention does not appear to have a positive impact on self-esteem or overall school adjustment; however, retention is associated with significant increases in behavior problems as measured by behavior rating scales completed by teachers and parents, with problems becoming more pronounced as the child reaches adolescence.Results indicate that grade retention had a negative impact on all areas of achievement (reading, math and language) and socio-emotional adjustment (peer relationships, self esteem, problem behaviors, and attendance).
Students who were retained or had delayed kindergarten entry are more likely to drop out of school compared to students who were never retained, even when controlling for achievement levels. Retained students have increased risks of health-compromising behaviors such as emotional distress, cigarette use, alcohol use, drug abuse, driving while drinking, use of alcohol during sexual activity, early onset of sexual activity, suicidal intentions, and violent behaviors." "Students rated grade retention as the most stressful life event, followed by the loss of a parent and going blind."