More than one million students enrolled in U.S. public schools share classrooms and playgrounds with their classmates but have no home to return to when the bell rings at the end of the day.

Many of them are in Florida, the fourth state with the largest number of homeless students, behind California, New York and Texas. The Sunshine State has seen a dramatic increase in the number of homeless children enrolled in its public schools over the past decade: from the school years 2005 to 2014, the figure grew from 29,545 to 71,446, a 142% increase.

It's not just a Florida issue: families with children have become one of the fastest growing segments of the homeless population nationwide, according to a 2015 report by Florida's Council on Homelessness.

One of the challenges in dealing with youth homelessness is visibility. It's relatively easy to identify homeless adults in the streets, whose numbers in Florida have dropped in the last years. But how does one identify a homeless student?

For one, they are defined differently than homeless adults. The public education system says that a student is homeless when he or she lacks "a fixed, regular, and adequate nighttime residence," or if they share a home with other people "due to loss of housing" or "economic hardship.”

The recent U.S. economic crisis provides some context to explain the increase in the homeless student population.

In September 2008, the financial firm Lehman Brothers collapsed, bringing on the peak of the Great Recession that had officially started in December 2007.

In Florida, the sales of single-family homes had slumped for three years in a row, and 2009 would be no different, with a 7% decrease.

The recession officially lasted just over a year and a half, ending in June 2009. But while the economy began its slow recovery, unemployment in Florida was at a 10.7%. By the end of the year it had increased to 11.2%, while the national rate stood at 9.9%. The state's unemployment rate remained in double digits for two more years.

This dire economic situation, combined with the historically low household median incomes in a majority of the counties with the highest rate of homeless students, may have tipped the balance against the students and their families.

Although the average household income in Florida varied little during the Great Recession, some counties did suffer major jolts. They include Madison, Gadsden, Hamilton, Lafayette and Okeechobee, where the average household income fell, in some cases, more than 20%.

The poorest families, with the lowest incomes, took longer to recover and return to pre-crisis levels, according to a 2015 report by PolicyLab and First Focus named "The Effect of the Great Recession on Child Well-Being."

One decisive factor seems to explain the phenomenon of homeless students. According to the Council on Homelessness, the “need of for available, adequate, and affordable housing” is the main cause of homelessness.

Many families lost their home due to the crisis. PolicyLab and First Focus estimate that, "near the peak of the crisis", one out of 46 properties in the U.S. was foreclosed. In addition, during the recession, about 2.3 million children in single-family houses lost their homes due to foreclosures.

Foreclosures were nothing new in Florida. In 2008, 10 counties in the state were among the areas with the highest foreclosure rates in the country. Only California had more counties with such high foreclosure rates, according to the Pew Research Center.

The recession hit the Sunshine State hard. At the end of 2012, Florida had “the biggest share of foreclosure inventory of any state,” according to RealtyTrac numbers cited in a report of the Office of Economic and Demographic Research.

That same year, Brookings and First Focus estimated that six million kids in the U.S. were “at risk of losing their homes,” while 40.9 million households nationwide were using more than 30% of their income to pay for housing.

In Florida, hundreds of thousands of families were spending much of their income in housing. In 2007, 577,242 homes were spending more than 40% of their income on rent. These were low-income households, with annual earnings 60% below Florida's median income. Six years later, that number climbed to 715,032 families, according to a study done by University of Florida's Shimberg Center for Housing Studies.

Nearly half, 44%, of all low-income homes in Florida -close to one million- were considered to be "extremely low income” in 2013.

For poor families who spend much of their resources to pay their housing, the problem is a lack of affordable housing opportunities in Florida. For every 100 extremely poor households, there are only 31 affordable and available units, according to a University of Florida report.

Some researchers say that public social programs were crucial to reduce the impact of the crisis on families and children. First Focus' study shows that many states maintained or increased their food aid during the recession, which, along with other kinds of aid, helped families keep their homes. But many of these programs are now suffering budget cuts.

From 2005 to 2013, the number of children that received food aid in Florida grew 135% to 1,380,248. The year with the highest increase was 2009, with 33%.

During those same years, a large percentage of children in counties like Hamilton, Gadsden, Putnam and Madison received food stamps. In those areas, more than 25% of the minors are African American. In Gadsden that figure is over 60%.

In Okeechobee, Osceola, DeSoto and Hendry, over 40% of children received food stamps every month in 2013. These are counties where the rate of Hispanic children exceeds 38%, compared to the 34% state average.

Living without a stable home has a physical, emotional and psychological impact on children. Homeless students are more than twice as likely to to have health problems and three times more likely to have severe health problems than children with homes, according to First Focus and PolicyLab.

Asthma and hyperactivity are the most common conditions among homeless children. They also have three times the rate of emotional and behavioral problems, like anxiety, depression, sleep problems, withdrawal and aggression, according to a report by Child Trends.

Being a homeless child also has an impact in their school performance: they are more than twice as likely as children with homes to be expelled or suspended, drop out of high school or repeat a grade, says the report.

To give an example: the Institute for Children, Poverty & Homelessness discovered that during the 2013-2014 academic year, only 17% of New York's homeless students reached the minimum academic standards in math. And recovering their homes doesn't guarantee an improvement in results. Among the children who were once homeless, only 20% achieved an optimal level in mathematics.