The NYPD Counterterrorism Bureau released a document pertaining to the Active Shooter phenomenon titled: NYPD Active Shooter Recommendations and Analysis for Risk Mitigation. (If you have difficulty with the link, just Google search the title). It is a PDF file document that has four parts and an Appendix.
Part I - Introduction
Part II - Recommendations
Part III - Analysis
Part IV - Analytic Methodology
Appendix - a compendium of a variety of 281 active shooter incidents in a variety of locations ; office, commercial business, factory . warehouse, SCHOOLS, and other locations.
THE SCHOOL ACTIVE SHOOTER INCIDENTS START ON PAGE 78 OF THE DOCUMENT.