A week-long inquiry carried out by Suffolk county council concluded that the school had highly effective and efficient systems for responding to a critical incident.
"The school's ethos of respect, openness and honesty helped develop a strong and secure culture in which pupils felt safe," it said. "This helped the school to continue in a calm manner and to work through the aftermath."
Five years ago, inspectors who visited the school, said pupils' behaviour was very good and a significant strength of the school.
As a result of the inquiry the council has updated its critical incident advice to schools. This included clarifying its checklist of what to do in an emergency and providing details to schools of how they can access long-term support.
David Thornton, acting director of learning for Suffolk, said: "This was a shocking incident that thankfully is very unusual.
"I hope that now the case is concluded the school will be able to build on its strengths and the respect it clearly enjoys in the community."