Shooting of 20 young children and six staff has failed to produce breakthrough on gun laws that seemed possible after tragedy

It was the moment that was supposed to change the stubborn politics of gun control in the United States. A year ago on Saturday, in a bucolic corner of Connecticut that was known for little except the quality of life enjoyed by its citizens, 20 young children and six teaching staff were killed as they began another ordinary day at Sandy Hook elementary school.

There had been horrors like Sandy Hook before. Aurora, Virginia Tech, Columbine – but this time, the age of the children involved seemed to hold a particular power. Such was the groundswell of support for reform of America's notoriously lax gun laws that it seemed the political logjam might finally be broken.

But in April, any hopes for a bipartisan effort to combat such gun violence were dashed in what the president, Barack Obama, described as a "pretty shameful day" for the Senate. After the most repugnant mass shooting in the nation, a bipartisan bill on background checks failed within five votes of passing the Senate.

A year on, amid vigils and memorial events for those murdered by Adam Lanza, who also killed his mother and himself, campaigners for gun control say they will once more push for Congress to act. They say they are picking up grassroots support, and that sweeping reform in states such as California is a template for what can be achieved.

However, an analysis of the legislative changes in the last year across the states shows an expansion of gun rights. Since December 2012, 27 states have passed 93 laws expanding gun rights, while only 43 gun control laws have passed, according to a map published by PBS Frontline and the Law Center to Prevent Gun Violence this week.

Gun control advocates say such statistics do not provide a true picture of the kind of progress they have made. Joint analysis by the Brady Campaign to Prevent Gun Violence and the Law Center to Prevent Gun Violence shows that, in eight states, there was sweeping gun reform in 2013.

The analysis shows that Connecticut, where the tragedy happened, Maryland, Delaware, Illinois, New York, New Jersey, Colorado and California all made significant changes to strengthen gun control laws, with five states passing new laws requiring background checks on all gun sales. Illinois also passed legislation allowing concealed weapons to be carried in public.

Newly formed groups such as Moms Demand Action for Gun Sense have amassed thousands of new members and have chapters all over the country. Americans for Responsible Solutions, a group run by Gabrielle Giffords, the former Arizona congresswoman who was shot in the head in a mass shooting in Tucson that killed six in 2011, raised $6.1m for gun control. Moms Demand Action have launched a powerful ad, backed by Mayors Against Illegal Guns, calling for an end to the "silence" over gun control. Laura Cutilletta, a staff attorney at the Law Center to Prevent Gun Violence, described the level of support for gun control advocates this year as "unprecedented".

Her group's main mission in 2014 will be to have another crack at getting background check legislation through Congress. The Brady campaign has said it is working with federal lawmakers to this effect.

They want to tighten rules that govern the sales of guns at gun shows and online, which are not currently subject to a background checks, and which make up 40% of all sales.

This year, gun control groups said they had spent five times as much on federal lobbying as they did the previous year. However, according to the Sunlight Foundation, the amount spent in the first six months of 2013, $1.6m, was still dwarfed by the $12.2m spend by the gun rights lobby, headed by the National Rifle Association (NRA). Both sides of the gun control debate also spent millions on television advertising and were active in the state elections.

Bill Allison, the editorial director of the Sunlight Foundation, told the Guardian: "One year later a lot of money has been spent and not a lot has changed. A few states have come out with stronger laws, but there have also been weakening of gun control laws and permits to carry."

Allison said that while the gun control lobby was beginning to see much more money than before, led by Michael Bloomberg, New York's outgoing mayor, and others, it was no match for the NRA.

"But what the pro-gun rights lobby has is grassroots, boots on the ground. They can mobilise people. They have been operating like this for decades. There was a belief, right after Sandy Hook, that the gun rights lobby was in disarray. The NRA had a few disastrous press conferences. But it is a well-oiled machine that has been around for years."

Allison is sceptical that gun control advocates have the clout they need against the NRA. "The gun control movement is very passionate but it is still not very organised," he said. "Even with the money, they still can't match the organisation, the email lists, the permanent advocates of the NRA."

Richard Feldman of the Independent Firearms Owners Association said that, following Newtown, "we squandered the opportunity to articulate the problem with the misuse of guns and to design policies accordingly". Feldman said he supported the final version of the Senate background check bill proposed in April and believed that had it started out that way, it would have got through. But because of previous measures proposed, including one put forward by the senator Dianne Feinstein, Democrat of California, to include an assault weapons ban, gun owners had already made their minds up to oppose it.

Her measure failed to make it to the final Senate bill.

"Much of the debate had centred on assault weapons and high-capacity magazines," said Feldman. "We think it is reasonable to provide for checks at gun shows just like gun shops. But frankly, I'll be damned if I'm going to run a background check on my wife or my daughter if they need a gun."