More than 1.1 million students in the United States were homeless in the 2011-12 school year – an all-time high, according to new data released by the Department of Education on Thursday.

Overall, 1,168,354 students enrolled in American preschools and K-12 schools were homeless. The number is a 10 percent increase from the previous year, and a nearly 75 percent increase since the recession began. The majority of states reported a year-to-year increase in the number of homeless students, and 10 reported increases of 20 percent or more between the 2010-11 and 2011-12 school years. In states such as Maine and North Carolina, the increases were as high as 53 percent. Only eight states (Oregon, Utah, Arkansas, Louisiana, Alabama, South Carolina, New Jersey and Connecticut) reported decreases in the number of homeless students.

"We're really alarmed by these numbers," says Cara Balardi, senior policy director at the children's advocacy group First Focus. "I think it's a sign that despite what we read in the news about the economy getting better and the recession being over, it's clear children and families are still suffering the effects."

The government data also comes on the heels of a new Census report showing nearly a quarter of children in the United States under the age of 18, about 16.1 million, lived in poverty in 2012. The report, released Sept. 17, showed that the poverty rate overall – and for children especially – shot up during the recession.

But the data, released by the department's National Center for Homeless Education, still underestimates how many American children are homeless. Infants and toddlers, as well as young children who are not enrolled in public preschool programs who may be homeless, are not counted. Additionally, older children who aren't enrolled in school, who have dropped out or run away are not captured by the Department of Education's data.

Balardi says that although there's no way to know entirely how many children are homeless, if those subgroups were taken into account, the number would be considerably higher, particularly because young families with younger children are disproportionately represented in the low-income and homeless populations.

Although homeless children receive assistance through local schools (such as runaway youth programs and designated homeless student liaisons), not all are eligible under the Department of Housing and Urban Development's definition of homeless, and are unable to receive support from HUD that could help homeless families and children find affordable housing.

People who are staying in a motel or with friends or relatives, or are wards of the state, do not qualify for assistance from HUD.

Jeremy Rosen, policy director of the National Law Center on Homelessness and Poverty, said in a statement HUD needs to "re-prioritize" the issue and "break down the definitional barriers that all too often prevent homeless children, youth, and families from receiving housing assistance."

Balardi says working to ensure families have access to affordable housing can help solve the problem of homelessness and improve homeless children's academic success.

That's because homeless children move frequently, and often fall behind in school as a result, according to Barbara Duffield, policy director of the National Association for the Education of Homeless Children and Youth.

"Yet education is the surest path out of poverty," Duffield said in a statement.

The government data shows that about half of homeless students in third grade through high school did not meet state proficiency requirements in reading or math in the 2011-12 school year. And those numbers are a slight decrease from the previous year. In the 2010-11 school year, for example, 52 percent of students in third grade through high school met or exceeded state proficiency levels, while 51 percent did so the following year.

"If we wish to prevent another generation of children from becoming homeless adults, we must meet their basic needs and ensure a stable, supportive school environment," Duffield said.