A teacher shortage that existed prior to the COVID-19 pandemic has become a nationwide issue, prompting parents to step in as substitute teachers in their children's schools.

Lisa Ursy is from Charleston, South Carolina, and is a substitute teacher at Murray-LaSaine Montessori School, where her partner is the principal and their children are in 7th and 8th grade. She is a career teacher, now retired.

Ursy told "Good Morning America" that being in the building has given her a "sense of calm and assurance because I can see everything."

Deciding to be an in-person substitute teacher during the pandemic was difficult, Ursy said.

"It was hard to make the decision to send our kids back to in-person during the time period cases were and are rising and not falling," she said. "Because Meredith [her partner] is the principal and because I know how seriously our family takes this pandemic, we all decided to go all in and make it as safe as possible."

Nicola Soares, the president of Kelly Education, a company that places substitute teachers in 40 states, told "GMA" the existing teacher shortage has been "exacerbated even further because of the pandemic. The vacancies for full-time teachers increased exponentially."

The company estimates some school districts have close to 1,000 vacancies.

Five schools in the Scottsdale Unified School District in Arizona were forced into remote learning on Monday because of a teacher shortage, ABC News affiliate ABC 15 reported. The station reported a letter went out to parents on Sunday that read, "Unfortunately, we have learned over the weekend that we do not have an adequate number of teachers or substitutes to cover all teacher absences tomorrow."

In Garland, Texas, a "Super Subs" program was launched to offset the shortage of substitute teachers during the pandemic and help support student learning. ABC News affiliate ABC 8 reported administrators at Garland Independent School District will leave the central office and head to the classroom at least once a week for the rest of the school year. Some days, nearly 45% of the requested substitute assignments are not filled, a district administrator said.

Patrice Pullen is another mom who has stepped into the role of a substitute teacher in her children's school, Lake Nona High School, in Orlando, Florida. Prior to subbing, she was building her real estate business. Her daughter is attending school virtually, but Pullen is teaching in person.

"They have me wherever the need is," she told "GMA." She's been in a French class and is about to start with a group of students who are at risk of not graduating. "I'm beyond excited to be their advocate and give them the support they aren't able to get at home."

While remote learning has been a struggle for parents, it's hard on the teachers, too.

"I see the work, the toll it takes on our administrators," Ursy said. "I see how hard the teachers, staff and kids are working. I see the awkward moments when adults and kids can't hear through muffled masks and plexiglass."

She said teaching during the pandemic adds another element to the job that wasn't previously a factor.

"The one thing I do know is that subbing during COVID isn't just subbing," she said. "It's like you are the kid's bodyguards, constantly reminding them to pull up their masks, stand apart and wash their hands."

The upside, in addition to the additional income, is "you can make a difference, maybe a big difference," she said. "I love being able to be a part of this team, this 2020 team."

Pullen agreed.

"You do it for the kids. You do it because you care," she said. "I am here for the kids; it's my way of giving back to my community. I'm not a bench warmer at all. I am all in."