Actually, after Congress tried to ban automatic weapons for private use (I forget the name of the Act, but we debated it when I tried out a pragmatic debate style) the number of school shootings with automatic weapons actually rose by large numbers, along with other automatic weapon-related crimes. I don't think it's the legal access to weapons that affects the amount of shootings, but rather the mentality of the shooters. Guns will always be available in one way or another, it's the people who use them that matter.
After all, the amount of people who own guns who actually go on shooting sprees is incredibly small. When we take that into consideration and note that 25% of American adults own at least one gun, for a total of 192 million firearms, of which 65 million are handguns, and then consider that only 12,996 murders were committed with firearms in 2010 in the United States, we then see that the base rate for a legal gun owner to commit a murder with said gun is equal to 12,996murders/77,897,979gun owners=0.0001% of gun owners using them to murder, or possibly even fewer of those gun owners committing more than one murder. Therefore, all the worrying about gun control every time there is a random shooting spree is irrational.
Of course, it is a very unfortunate event that took place, but if we're going to ban what has the chance to cause harm just because people misuse them, we might as well ban kitchen knives, hammers, and baseball bats as well. All of these can prove to be very lethal in the wrong hands, and they all have murder rates of their own.