At least 10 times in the last two months, crackling gunfire just outside the Uere special needs school has sent students and teachers diving to the floor as heavily armed gangsters warred among themselves and sometimes with police in the Rio slum of Mare.

With rival drug dealers on practically every corner and a militarized campaign by authorities to take them out, shootouts have become so common that the school holds drills for students to practice taking cover quickly.

"After (a shootout) it's not possible to teach," said Yvonne Bezerra de Mello, the founder of Uere, which offers classes for underprivileged students with learning difficulties. "So we just play and talk, because some of the children get really nervous."

In this April 5, 2017 photo, students sit in their classroom at the Uere special needs school in the Mare slum in Rio de Janeiro, Brazil. "The children aren't safe anywhere," said Yvonne Bezerra de Mello, the founder of Uere, "They wake up to the so… — In this April 5, 2017 photo, students sit in their classroom at the Uere special needs school in the Mare slum in Rio de Janeiro, Brazil. "The children aren't safe anywhere," said Yvonne Bezerra de Mello, the founder of Uere, "They wake up to the sound of gunshots and go to bed to the sound of gunshots. ... They see death at every corner." (AP Photo/Silvia Izquierdo)

In this April 5, 2017 photo, Yvonne Bezerra de Mello embraces a girl in the Uere school at the Mare slum in Rio de Janeiro, Brazil. "After (a shootout) it's not possible to teach," said Bezerra de Mello, the founder of Uere, which offers classes for… — In this April 5, 2017 photo, Yvonne Bezerra de Mello embraces a girl in the Uere school at the Mare slum in Rio de Janeiro, Brazil. "After (a shootout) it's not possible to teach," said Bezerra de Mello, the founder of Uere, which offers classes for underprivileged students with learning difficulties. "So we just play and talk, because some of the children get really nervous." (AP Photo/Silvia Izquierdo)

Brazil's most famous city has long struggled with violence, particularly in the hundreds of slums controlled by drug traffickers. But amid a punishing economic crisis, some studies suggest 2016 was Rio's most violent year in decades despite a police pacification program that was meant to curb slum violence ahead of last year's Olympic Games.

Crime still seems to be rising: In January and February, homicides rose 17 and 24 percent, respectively, compared to the same months last year, according to Rio state government crime statistics.

And schools are increasingly caught in the crossfire.

Every day, shootouts force the closure of between 20 and 30 schools or day care centers, according to Cesar de Queiroz Benjamin, the city's public schools chief, resulting in 6,000 to 7,000 children being sent home. If this rate continues, Rio will far exceed the 1,500 closures it saw last year.

"It has clearly gotten worse," Benjamin said.

The toll the violence takes on children attracted national attention on March 30 when a 13-year-old girl was shot and killed at a school in Acari, a poor northern neighborhood, when she was caught in the crossfire of a lengthy shootout between police and gangsters.

Maria Eduarda Conceicao was hit by several rounds at the school entrance as she walked to the water fountain after physical education class. Large bullet holes can still be seen on the school's outer wall and front gate, a grim reminder for students, teachers and parents arriving every day.

An autopsy confirmed one of the bullets that hit Conceicao was a 7.62 mm round, fired from a military-grade rifle in the hands of police. Cellphone video shot by a bystander and widely circulated in local and social media showed two officers continuing to fire at armed but apparently wounded suspects lying on the ground in front of the school. The two officers have been indicted in the killings.

When the video is magnified, Conceicao's lifeless body can be seen on the school grounds.

"We should all feel very humiliated and ashamed," Rio de Janeiro Mayor Marcelo Crivella said after attending Conceicao's funeral this month. "This cannot happen again."