OBJECTIVE: Clinical reports suggest that many adults who engage in self- destructive behavior have childhood histories of trauma and disrupted parental care. This study explored the relations between childhood trauma, disrupted attachment, and self-destruction, using both historical and prospective data. METHOD: Seventy-four subjects with personality disorders or bipolar II disorder were followed for an average of 4 years and monitored for self-destructive behavior such as suicide attempts, self-injury, and eating disorders. These behaviors were then correlated with independently obtained self-reports of childhood trauma, disruptions of parental care, and dissociative phenomena. RESULTS: Histories of childhood sexual and physical abuse were highly significant predictors of self-cutting and suicide attempts. During follow-up, the subjects with the most severe histories of separation and neglect and those with past sexual abuse continued being self-destructive. The nature of the trauma and the subjects' age at the time of the trauma affected the character and the severity of the self-destructive behavior. Cutting was also specifically related to dissociation. CONCLUSIONS: Childhood trauma contributes to the initiation of self-destructive behavior, but lack of secure attachments helps maintain it. Patients who repetitively attempt suicide or engage in chronic self-cutting are prone to react to current stresses as a return of childhood trauma, neglect, and abandonment. Experiences related to interpersonal safety, anger, and emotional needs may precipitate dissociative episodes and self-destructive behavior.

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This is one of many studies that I believe have been conducted.  Although it does not specifically address elementary aged kids, it does speak to the general phenomenon of self harm. I think the important point is that irregardless of a child's age, self harm is often attributable to sexual abuse and major trauma (such as physical and emotional abuse as well as neglect).  Most of these kids also have attachment issues. So, it is generally not simply a matter of parental separation.  Although that can certainly be a source of stress and trauma for a child, I believe that there is often something deeper going on that can account for the behavior.