Especially considering the fifth amendment was specifically intended to allow for a militia to defend against the government, not to enable students to carry an automatic rifle into school—but here we are
2nd amendment, 5th is the "right to remain silent" etc.
Still, the issue with school shootings is mostly that it targets the wrong people. After school programs, community support for troubled youth, options for local service or a job placement program for kids would all be solutions, but the youth only sees other kids at school as the problem. If the system is so screwed up that a kid feels the need to take up arms to fight against it, then they should, but school shootings are unnecessarily cruel and generally fail to lead to progressive changes; more often than not they become justification for increases in the very authoritarian measures that promote the violence in the first place.