The shooting at Robb Elementary School in Uvalde, Texas, last May in some ways changed the conversation yet again on gun violence in the United States: 19 fourth-grade students and two teachers died in one of the deadliest school shootings in American history.

But what made the Uvalde attack extraordinary was not just the death toll. It was the fact that more than 370 officers from local, state and federal agencies had responded to the scene — some standing in the school hallway — but allowed the gunman to remain holed up with students inside the school for 77 minutes before storming in to kill him.

In the aftermath, that left a host of questions, not only about the laws governing access to guns but also about police training, emergency responses, school security and preparedness, and who ultimately would be held accountable for a failure that occurred on so many levels.

In the year since the attack, a number of people have resigned or lost their jobs. New laws have been debated, and some have been passed. Criminal investigations have been opened. Survivors have undergone months of physical therapy.

Those who did not survive have been buried.

Did any of it make another mass shooting less likely? In Uvalde, people have had their doubts.

“Almost a year now, and honestly nothing has changed,” Jesse Rizo, the uncle of one of the massacre victims, told the Uvalde school board in the weeks before Wednesday’s anniversary of the shooting.

The gunman climbed a low fence and entered the school through what turned out to be an unlocked door at around 11:30 a.m. that Tuesday, as students in the classrooms mainly targeted, Rooms 111 and 112, were watching movies. Within minutes, several officers, including the chief of the small school police force, Pete Arredondo, arrived and followed the sounds of gunfire to the two classrooms. Two officers were grazed by bullets as they approached one of the classroom doors and pulled back.

Mr. Arredondo made the decision to treat the situation not as an active shooting but as a barricaded subject incident, and a decision was made to wait until a heavily armed tactical team from the Border Patrol arrived with better equipment to breach the classroom.

Steven McCraw, the head of the Texas Department of Public Safety, immediately laid most of the blame on Mr. Arredondo for the delay, but a special Texas House committee report on the shooting found that the failure was “systemic,” noting that scores of officers were there and that they also failed to act, even as children were dialing 911 from inside the classrooms.

Would a faster police response have saved lives? There is still no clear answer to that question. The victims suffered terrible injuries and most appear to have died right away. But some died on the way to the hospital and in a final footnote in the report, the committee concluded, “It is plausible that some victims could have survived if they had not had to wait” for rescue.

Mr. Arredondo was among the first to go, when the school board voted unanimously in August to fire him, to the sound of cheers and claps in the packed school auditorium. Lawyers for Mr. Arredondo, who has said that officers reasonably focused on preventing the bloodshed from expanding to other classrooms, called his firing “an unconstitutional public lynching.”

The school district later dismantled its entire police force, which consisted of five officers, and is still in the process of revamping it with new hires.

The city police force did not emerge unchanged, either: The lieutenant who was in charge on May 24 while the police chief was on vacation, Mariano Pargas Jr., stepped down in mid-November after 18 years in the force.

And amid pressure from the families of the 21 victims, Hal Harrell, the school superintendent, retired in the fall. He was replaced in the interim by Gary Patterson, a former superintendent from San Antonio.

The Texas Department of Public Safety, the state police agency that includes the Texas Rangers, also took steps to push out at least two out of the seven officers who were under investigation for their role in the response, including Sgt. Juan Maldonado and a Texas Ranger, Christopher Ryan Kindell, although some of those investigations are still pending.

The local district attorney, Christina Mitchell, is still looking into whether criminal charges should be brought against any of the police responders. Ms. Mitchell has said that she intends to present any evidence of criminal wrongdoing to a grand jury. No decision is expected for months.

Investigations are also still pending from the Justice Department and the City of Uvalde, which has hired an independent investigator.

“Everybody that was there that day has to be held accountable,” said Uvalde’s mayor, Don McLaughlin.

The response by officers in Uvalde has been broadly condemned. But it has not resulted in immediate changes to how police officers are trained in Texas. Last July, Mr. McCraw, the state public safety director, said his agency would “provide proper training and guidelines for recognizing and overcoming poor command decisions at an active shooter scene.”

But several policing experts said that creating that kind of training presented a challenge because countermanding orders from an incident commander went against the very orientation of most police departments. And the state has yet to roll out new training based on last year’s directive.

In the meantime, the focus has been on increased safety precautions and better equipment. In Uvalde, local police now have additional ballistic shields and helmets, as well as new tools for breaching barricaded doors. At schools in Uvalde, school administrators have installed new eight-foot fences, sensors that would alert staff if a door did not lock properly and more security cameras to monitor activity outside all schools.

The school where the attack occurred sits behind chain-link fencing with its windows boarded over, and is slated to be demolished as soon as lawsuits and the pending investigations are concluded. Ms. Mitchell, the district attorney, and many victims’ families are among those taking legal action to block the demolition of the school until there is no further need to collect evidence from the crime scene. Mr. Patterson, the interim superintendent, said plans for a permanent memorial were under discussion, but it has not yet been decided what and where that would be.

A new elementary school is to be built three miles from where Robb Elementary now sits. The new school, which does not have a name yet, is scheduled to open its doors in 2024, said Eulalio Diaz Jr., a member of an advisory committee overseeing planning for the new campus. Early designs include the colors of papel picado, the traditional Mexican folk art that features multicolor sheets of paper — in recognition of the Hispanic culture that has long been a large part of Uvalde, and the families at Robb Elementary.

For now, Robb Elementary’s students have been dispersed to other schools.

Texas has moved to widen access to firearms in the year since the shooting.

Months before the attack, Texas lawmakers did away with permit requirements to carry handguns. After the attack, the state also effectively lowered the age required for carrying a handgun to 18 from 21, once officials stopped defending the higher age limit in court in December.

There had been slight movement in the Legislature in early May, when a bill that would have raised the age to purchase an AR-15-style rifle to 21 from 18 received a favorable vote in a House committee. The legislation would possibly have prevented the 18-year-old gunman in Uvalde from purchasing the weapon he used in the massacre.

But the bill missed a key deadline and failed to receive a vote in the full Texas House.

Elsewhere in the country, there has been a mixed record on gun control laws proposed since Uvalde, with access restricted or expanded depending on which party is in control.

Washington State, where Democrats control state government, last month became at least the ninth state to join efforts to prevent the distribution of AR-15s and other powerful rifles often used by mass shooters, after the earlier lead of states like California, New York, New Jersey, Connecticut and Massachusetts.

Republicans have moved in the opposite direction, with lawmakers in several states introducing legislation to expand the ability to carry concealed weapons without a permit and eliminate such things as gun-free zones.

Last summer the U.S. House of Representatives passed a bill that would have reinstated a federal ban on assault weapons, but it stalled in the Senate.

Also last summer, Congress passed a new federal gun bill that brought the often-divided legislature together, galvanized by the tragedy in Uvalde. Democrats and just enough Republicans approved a measure that enhances background checks for potential gun buyers under 21, allowing law enforcement agencies to check juvenile records, including mental health records, starting at 16. President Biden has signed it into law.

The law also provides millions of dollars for states to put red flag laws in place, strengthens laws against straw purchasing and trafficking of guns, and provides funding for mental health crisis intervention.

Gun violence activists, including the Uvalde families, said they planned to return to Washington, D.C., to lobby for a total ban on assault weapons.

J. David Goodman contributed reporting.