Tragedy at Sandy Hook Elementary

The recent event at Sandy Hook Elementary school where 20 innocent children were murdered in their classrooms is devastating to everyone.  These were all innocent babies ages 6 and 7 and a shameful loss of life. A lot of investigation will be done for days, weeks, and perhaps months to come. What should school systems do? Some suggest that school principals and teachers should have guns in their classrooms. Is that really an answer? I worked in an organization where the security department were having a meeting and a disgruntled security office used his service pistol to kill the supervisor and shoot others at the meeting.  They all had weapons. Should the school system have a resource officer at every school, elementary, middle and high?  What do you think?  What are the options?