Prove it. Here's a link to the data: https://www.gunviolencearchive.org/reports/mass-shooting
Of the 4 mass shootings that happened yesterday, none of them seem to have happened in a gun-free zone. 29 people were injured and 4 killed in those 4 incidents. And, interestingly, there have been 5 mass shootings in Texas (a state with weak gun laws), since the last mass shooting in California (where the gun laws are stronger). It kind of suggests that gun laws work.