Over the past six months, about 1.5 billion children around the world have been told to stay home from school to help minimize transmission of the coronavirus. More than 30 percent of these students — around 463 million — were unable to gain access to remote learning opportunities when their schools closed, according to a report on Wednesday by Unicef, the United Nations agency for children.

“The sheer number of children whose education was completely disrupted for months on end is a global education emergency,” Henrietta Fore, the executive director of Unicef, said in a statement. “The repercussions could be felt in economies and societies for decades to come.”

Schoolchildren in sub-Saharan Africa have been the most affected, the report said, as education systems there have failed to reach about half of all students through television, radio, internet or other forms of remote learning. Many children in the region have gone without classes of any kind since March, according to a separate report published Wednesday by Human Rights Watch.

In part to address this unequal access, education officials in Kenya said last month that they were canceling the academic year and making students repeat it.

Forty percent of students in the Middle East and North Africa, 38 percent in South Asia and 34 percent in Eastern Europe and Central Asia have also been unable to learn remotely, according to the Unicef report, which said children in rural areas had been disproportionately affected.

In general, students from higher-income households with more educated parents seem to be faring better at studying at home, researchers around the world have found. This has reinforced concerns that school closures may be yet another way that longstanding inequalities will be exacerbated by the pandemic.