The loaning thing is completely unreasonable.
There are so many guns in the population now, and guns last so long, that doing anything now to limit who has them is all but unenforceable except post-crime, which is meaningless because these school shooters are all killing themselves.
It would be more feasible, though costly, to put metal detectors and guards at all doors of high schools (I know school shootings aren't just at high schools, but the majority are).