First off, you didn't say "school" originally, you just said mass shooting and there have been several in the UK since the gun ban; also it doesn't matter if innocent people are killed at a school or elsewhere, what matters is that they were killed. Secondly, the "zero deaths" shooting had 12 wounded; the lack of deaths wasn't for a lack of trying and I'm sure those people would have preferred not to have been shot. Thirdly, most of those American mass shootings in the Wikipedia article aren't mass shootings in that they aren't some crazy killing random strangers, they are gang violence; you may as well include all of the UK's gang homicides then. Many of the school "mass shootings" also had no deaths. For example, Wikipedia counts this as a school shooting: "An individual who was not a student accidentally shot himself in the leg in the parking lot of Glades Central High School". No reasonable person can say that is the same as what happened in Texas, and dozens of the "school shootings" in the list are similar to the parking lot accident.

The deadliest mass shooting of all time happened in France in 2015 and the second deadliest happened in Norway in 2011 (yes, deadlier than any American mass shooting). Europe has had a large number of mass killings. Here's a PARTIAL list (since there are no activist groups compiling lists of "mass" "shootings" in Europe like there are in the US, it's difficult to find them without scanning old news articles) of SCHOOL shootings in Europe over the last twenty years (and yes it is fair to compare the US to all of Europe due to population and size; European countries are equivalent to American states (which have varying degrees of gun control)): https://news.ycombinator.com/item?id=31515008. Additionally, there have been a lot of European mass killings that weren't targeted at schools like the Manchester Arena Bombing, Charlie Hebdo, the aforementioned Bataclan and Oslo massacres, the Nice truck attack, the various vehicle ramming attacks in London and elsewhere in Europe, and more. Your gun bans haven't prevented crazies from killing massive amounts of innocents, neither with guns nor with other methods.