I would also consider other methods of self harm in an elementary age kid. My self-harm was serious head banging and hitting myself in the head and other parts of the body with craftsman tools and my fist. I didn't cut at elementary school age. In fact I almost never cut unless I was totally dissociated and had no idea I had done such a thing (which only happened once). That is why I got rid of my swiss army knife on my key-ring. Self-harming in younger kids can include not eating/food restriction (anorexia)or eating and purging (bulimia) and I really think head banging is common especially when your trauma starts when you are really young. You learn at a young age and that self-harm (which I really think of as "letting out rage" or dissociative terror) allows for two things
1. You can let out the rage you feel at your parents (which you otherwise cannot do).
2. It is a huge emotional release.
Not research based just my own experiential observations.