It is very expensive to fail students and thus add a year, or more, onto their schooling. Undoubtedly this accounts in part for the willingness of some administrators to promote students whom teachers have tried to fail. But if we are talking about the costs of retention to the students themselves and to society, we should also look at the costs of promoting students who have not met the minimum standards that most schools require. The harm of social promotion is compounded for children who make a slow start in school. The truth is, social promotion is a lousy idea.
Standards only work if everybody can see that they mean something.
If you have many, many failures, there will be tremendous political pressure to return to social promotion. To sustain the ability to hold students back, you must have a system of supports to keep failures low. But you must be willing to fail the few students who don't meet the standards, despite all you can do to help. The best way to keep this from happening is to identify children who are not learning basic skills very early in their school career and offer them extra help before they fall behind and get used to failure. There are various ways of doing this.