Determine why your child is struggling. Does the difficulty stem from a temporary problem (personal or academic), or is it ongoing?
Assess the severity of the problem. Could your child make up the work with extra credit projects or summer school classes?
Consider all the options. For an older child in middle school or high school, perhaps dropping down to a less demanding track in major subject areas would give your child enough breathing room to pull his work up to par.
Involve your child in the decision. His reaction to the idea of retention may give you some valuable clues to the situation. For example, an overplaced child who has struggled in school for months or even years may express relief at the prospect of stepping off the treadmill.
Make sure you understand whether the school is recommending that your child be retained, or if the school cannot promote him because of failure to meet minimum standards. Except in the latter case, which is rare, the final decision is up to you and your child.
Prepare your child for the reality that he may suffer socially from a decision to repeat a grade. Emphasize the potential to offset these negatives with increased self-esteem when he experiences academic success, often for the first time.