There’s going to be a lot of “takeaways” from this I suspect. Many will be helpful, like locking back doors.
Sadly, one of Texas’ senators (Senator Ted Cruz) already proposed reasonably effective changes such as bullet proof glass, single points of entry at schools, an armed guard and the like - only to have it shot down by the Democrats.
This was completely preventable and it appears that it could have been fully funded across the entire country for less than half a billion.