As 56 million school children return to the classroom, the debate over masks in school rages -- along with the Delta variant.
"The Delta variant is really effective at making copies of itself," says John Brownstein, an infectious disease epidemiologist and ABC News contributor. "And from that, every cough or sneeze has more virus particles, meaning that you can more easily infect other people when you're sick."
According to the CDC, a person infected with the original strain of COVID-19 could infect two people -- it's about as transmissible as the common cold. With the Delta variant, that risk of spreading grows to at least five people.
"This is why we need these layers of intervention to keep our kids safe," Brownstein, told ABC News.
To visualize the potential ways schools can help curb transmission, Good Morning America Investigates teamed up with MIT Engineering Professor Lydia Bourouiba.
New 3D animations show how the virus can spread in a classroom of unmasked students.
"If we're not wearing a mask, that contamination is building up, particularly when we're in a classroom for hours," Bourouiba said. "But there are simple measures when we bring in fresh air from the outside that are very effective."
Bourouiba says than an open door and window increase the airflow. That helps clear the air out of the room but issues a warning about creating hot zones in the classroom.
"It's very important when we do that to not have a student sitting next to the inlet of fresh air, for example," Bourouiba said. "If that individual turned out to be infected, that could be a problem."
She also advises against placing students near the exit point as well, because that one student could be exposed to air that's loaded with particles exhaled by the entire class.
The professor, who has advised schools around the world, says those plastic dividers that put students in individual pods may do more harm than good.
"We are keeping the particulates longer in that room because we are hindering the airflow mixing that we want to create," Bourouiba said.
Instead, she suggests staggering the desks so a student is not seated directly in front of another student's breathing zone, especially if they are unmasked. But experts say improved room layout along with masking is the best combination.
"We have found time and time again is that masking can limit the spread of transmission. And especially indoor settings like schools," Brownstein said.
GMA and Florida Atlantic University engineers first demonstrated the efficacy of masks last year using a mannequin and green smoke to simulate a cough or sneeze.
That demonstration also highlighted the dangers of half masking, which leave the nose vulnerable to any potential viral particles floating in the air.
"What I'm especially concerned about for this school year is the gatherings that kids will take on in schools," Brownstein said. "So auditoriums, lunchrooms, gymnasiums, these are all places where you could see super-spreading events."