There are several problems with this analysis. First, school shooters are a fairly recent development whereas absent fathers have been around a long time. Second, if absent fathers were the problem, I would think the majority of shooters would be black since they have very high rates of fatherlessness. School shooters who are black are very rare. IMO the rise of school shooters reflects the rise in the number of kids who do not believe in God. Belief in God means that you will be punished for what you do in life and that moderates behavior. Those that dont believe do not fear the consequences of their deeds after death. They know they can avoid consequences simply by killing themselves, which they almost always do. Couple this with the desensitization to killing people they get from video games, movies and a high level of anger in general and have a school shooter.
What about the number of "Juvenile shooters" in general? If you have a group of individuals that is prone to a bad behavior then is seems that hey would engage in that behavior where they are frequently. If Blacks are dropping out of schools at a higher rate they might engage in the shooting in their neighborhood.
I think we need to compare apples to apples. I worked in an urban Juvenile detention facility for a while and I can only recall one white prisoner in for a shooting. ALL of these kids came from single parent homes.