Poor classroom ventilation is linked to lower math and reading scores, according to a new study that evaluated indoor air quality at K-12 schools in the United States.

Researchers say the findings, published May 4 in Science of the Total Environment, could help school districts prioritize renovations and inform designs of future buildings that promote student learning.

"For a child, they spend around one-third of their time in the classroom for at least 12 years," said study co-author Josephine Lau, an associate professor in the Durham School of Architectural Engineering and Construction at the University of Nebraska–Lincoln. "Generating a good learning environment for our next generation to succeed and thrive in learning is very important."

Inside homes and classrooms, air quality takes a hit from particles and toxins emitted from building materials, furniture, secondhand smoke and cleaning products, and a lack of fresh air causes these pollutants to build up indoors.

Although outdoor air pollution is also a concern in many areas, Lau said that the problem is usually worse inside.

"Unless the school is very close to a highway or close to a construction site or polluted industry plant, opening up the window and bringing more outdoor air is beneficial because it is usually cleaner than indoor air," she explained. 

A handful of prior studies showed that airy classrooms are associated with higher student performance. But most of this research measured ventilation rates or carbon dioxide levels as indicators of air quality, without considering other chemicals or particles.

To gain a more comprehensive look at the links between indoor air quality and student learning, Lau and her colleagues studied 220 classrooms in 39 schools in the Midwest over one year.  

The team looked at the type of classroom ventilation system and ventilation rate and measured air pollutants such as carbon monoxide and ozone. The researchers also looked at coarse and fine particulates in the air, the smaller of which can penetrate deep into the lungs and cause respiratory problems and other diseases. The study authors measured air quality parameters in the fall, winter and spring, and at the end of the academic year, the team collected final reading and math grades as indicators of student performance.

­­­­An important finding was that the type of classroom ventilation system was linked with mathematics performance. Students in buildings with centralized ventilation systems, which serve multiple rooms and usually have high airflow rates, had higher math scores than peers in classrooms with unit ventilators.

"The unit ventilator is like what you see in the motel," Lau said. "They have the unit right under the window, and it sucks air directly through that external wall. All the mechanical parts are right in the room, and usually they don't deliver as high of a ventilation rate."

Another problem with unit ventilators is that they tend to be very noisy because the system's motor and fan are located in the classroom itself, and background noise is known to adversely affect student learning.

The researchers also measured other aspects of the classroom environment that could influence learning performance, including noise, temperature and lighting, but Lau said that the team is still analyzing that data.

Another finding noted in the study was that ventilation rates in the fall and spring were associated with better student reading scores, and as the number of "gifted students" in a class increased, greater airflow had a larger impact on reading performance. 

According to Lau, it's not clear why gifted students appear to reap greater rewards from fresh air, but she said this finding highlights that it's important to consider that different people could respond to environments differently. For example, other research groups found that test scores of students from low-income families or those in which English was a second language suffered most from noisy classrooms. 

Another result from the study, which came as a surprise to the researchers, was that classrooms with higher particle counts were associated with higher student math scores.

"We didn't understand why a more polluted room has a higher learning outcome," Lau acknowledged. 

The researchers suspect that this counterintuitive finding could be due to different teaching methods. For example, hands-on "active learning" activities are known to help students retain knowledge, but movement from these activities may also stir up particles and worsen air quality.

Lau said that there are a couple of different reasons why poor air quality can affect learning performance. Exposure to pollutants can affect the ability of students to concentrate on mentally demanding tasks. In addition, poor air quality may reduce the overall health of students, leading to more school absences and fewer opportunities to learn class content.

According to Lau, this research could ultimately help schools with limited budgets to rank the importance of remodeling projects based on relevance to student learning. 

"For example, increasing ventilation rate should be ranked at high priority because we find a strong association [with student learning], and a lot of classrooms are not doing sufficient ventilation right now."

Lau and a colleague previously reported that only 30% of classrooms in the new study met recommended ventilation rates for acceptable indoor air quality, as set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

"Another thing that we also think this will be beneficial for is future designers or engineers who are designing the next generation of classrooms," Lau said. "This study will help them to set up criteria or parameters that will help improve the student learning."

The study, "Identifying the K-12 classrooms' air quality factors that affect student academic performance," published May 4 in Science of the Total Environment, was authored by Adel Kabirikopaei, Josephine Lau, Jayden Nord and Jim Bovaird, University of Nebraska-Lincoln.