KATIE CAMPBELL: When you think of a school, you might imagine something that looks like this. But many students actually spend a lot of time in buildings that look like this, this, and this.

STUDENT: Portables are definitely a problem. I have been in portables for around seven years.

KATIE CAMPBELL: These prefab structures are the go-to quick fix when school populations surpass a school's capacity. Compared to permanent school buildings, portables are about a third of the cost to construct. And they only take a few of days to install, compared to the many months it takes to build brick-and-mortar schools. But more than a few children we found are sick of studying in portables.

HANNAH PETERSON, Student, Kalles Junior High: It feels like you have got your priorities out of order, and I feel a little bit ignored.

KATIE CAMPBELL: Portables are supposed to be temporary; something to help schools deal with overcrowding until student numbers drop or new schools can be built. Try telling that to Billie Lane.

BILLIE LANE, Teacher, Kalles Junior High: Pass this forward.

KATIE CAMPBELL: She's been teaching in this portable classroom at Kalles Junior High in Puyallup, Washington, for 16 years.

BILLIE LANE: The one advantage of a portable is the walls are like — it's like one big bulletin board. You can put it up anywhere and leave it. So the kids have left their mark.

KATIE CAMPBELL: Her students call it Lane's world.

BILLIE LANE: This one's going on the wall.

KATIE CAMPBELL: They say a dynamic teacher helps make up for the shortcomings of portable life. But Lane admits not all portable classrooms are as cozy as hers.

BILLIE LANE: In some of the other portables that I have been in, smell has been an issue. You walk in and they have a real bad odor in them. The lighting is really bad. It's dark. It's dank. When it's that kind of an atmosphere, it sets a tone.

KATIE CAMPBELL: And it turns out portables actually can be harmful to student health.

Dave Blake is an indoor air quality specialist for the Northwest Clean Air Agency. He's tested air quality in more than 3,000 classrooms in Washington state.

DAVE BLAKE, Northwest Clean Air Agency: We have a lot of fancy equipment, but you don't really necessarily need it. You can walk into a classroom. And, right away, if you can smell the humanity and taste the humidity, you know you have got a ventilation issue.

KATIE CAMPBELL: Blake measures carbon dioxide levels first.

DAVE BLAKE: About 1,400 coming in. Fresh outside air is about 400 parts per million now worldwide. We like to keep classrooms below about 800 or 1,000 parts per million. So if it's above that, we want to know why.

KATIE CAMPBELL: High CO2 indicate that students are breathing too much of their own exhaust. They're taking in germs from coughs and sneezes that hang in the air.

Other airborne particles are likely building up as well, things like dust and allergens, or volatile organic compounds like formaldehyde. The

Tacoma-Pierce County Health Department is one of the few Washington State agencies with consistent CO2 data for schools. They found that on average portable classrooms didn't meet the federal standard for acceptable CO2 levels in spaces used for human occupancy.

DAVE BLAKE: CO2 is dropping in here with the kids gone.

KATIE CAMPBELL: Other studies show that, as CO2 levels rise, student performance falls.

DAVE BLAKE: As CO2 goes up, so does absenteeism. And it's notable that it's a little worse in portables, but we don't know why.

KATIE CAMPBELL: Blake also looks for signs of moisture by using infrared cameras and moisture meters.

DAVE BLAKE: Eight percent, that's essentially bone-dry.

KATIE CAMPBELL: When a building takes on water, there's likely to be mold, a common trigger for asthma. Problems get worse as portables age. Yet schools often use them well beyond their life expectancy.

Critics say portables should be reinvented. They should be made from formaldehyde-free, nontoxic materials. They should have open ceilings, larger windows, skylights, and solar panels to generate electricity. Instead of noisy HVAC units, they should have natural ventilation systems that exchange more fresh air.

But a portable like this is out of reach for most schools. Rudy Fyles is the chief operations officer for the Puyallup School District; 20 percent of their classrooms are portable. That's four times the national average.

RUDY FYLES, Puyallup School District: Portables are considerably less expensive than permanent space.

KATIE CAMPBELL: But those savings are only short-term. Studies show that over the course of their lifetimes, portables actually cost twice as much as typical permanent classrooms. In addition to higher maintenance costs, portables are also highly inefficient and take more energy to heat and cool. And because portables are independent structures, they often are charged residential electricity rates.

RUDY FYLES: It's kind of a double whammy. Not only do you use more power, but you pay a higher rate for the power you're using.

KATIE CAMPBELL: Portable classrooms aren't going away anytime soon. But there might be a solution on the horizon.

One of the greenest portables is being installed in a Seattle elementary school. In this time-lapse video, we're seeing the first portable classroom built to meet the Living Building Standards, the world's strictest rules in sustainable building.

RIC COCHRANE, Co-Founder, The SEED Collaborative: What we're trying to do is take something that was previously the weakest aspect of the school and turn it into a true asset.

KATIE CAMPBELL: This classroom is designed to generate its own energy and harvest its own water. Inside, the classroom looks fundamentally different.

RIC COCHRANE: You guys want to start with a little bit of show and tell?

KATIE CAMPBELL: Ric Cochrane helped design this classroom. Today, he's showing it to some fifth graders for the first time.

RIC COCHRANE: You will see that all of this is exposed, and we do that because we want to show how the structure is made.

JOEY CLARK, Student, The Perkins School: And what's that white thing up there?

RIC COCHRANE: That white thing is a carbon dioxide monitor, so we make sure that the air quality is good.

JOEY CLARK: And it has little gauges and knobs and tubes everywhere that — that are just really cool to look at that you would never find that in a building that had that all covered up, because it looks ugly.

RIC COCHRANE: We wanted to play with the center beam, which is structural here. And, again, that's also sustainably harvested wood.

ZOE BARNES, Teacher, The Perkins School: When they see systems like are in this building, that will encourage them to ask questions. And, for many students, that will encourage them to just poke around.

RIC COCHRANE: We're trying to expose things to make every single part of the building a learning opportunity.

KATIE CAMPBELL: Right now, the price tag is about $200,000. That's more than twice the cost of a conventional portable. Over time, they say lower operations and maintenance costs will more than make up the difference. For the kids who will get to use this space, the difference is priceless.