In a report published on its website, UNICEF said Nigeria's rapid population growth has stretched the educational sector beyond available resources.
The UN children's fund said this has led to as many as 4.7 million children being denied access to education.
"Forty per cent of Nigerian children aged 6-11 do not attend any primary school with the Northern region recording the lowest school attendance rate in the country, particularly for girls," UNICEF said.
"Despite a significant increase in net enrollment rates in recent years, it is estimated that about 4.7 million children of primary school age are still not in school."
It also noted that increasing enrolment figures have further stretched available educational facilities.
"Increased enrollment rates have also created challenges in ensuring quality education and satisfactory learning achievement as resources are spread more thinly across a growing number of students.
"It is not rare to see cases of 100 pupils per teacher or students sitting under trees outside the school building because of the lack of classrooms."
Several stakeholders have called on the Federal government to increase funding for the educational sector in order to address the obvious challenges.
In a recent article published by Naij.com, renowned Nigerian social media expert and columnist, Japheth Omojuwa, called for a radical change.
"Something is wrong with our system and content of education, and that thing has been wrong for a long while," he wrote.
"The system and the content of our education need a complete overhaul.
Even more recently, a professor of political science at Brooklyn College, United States of America, Mojubaolu Olufunke Okome, advised President Muhammadu Buhari to allocate at least 30 percent of the budget to the education sector.
“Education ought not to be left to pure market forces," Okome said.
"Government should fund education very well."
Her recommendation comes on the heels of several others from renowned education who feel that the number one challenge of the sector is funding.
This aligns with UNICEF's submission that "facilities and teachers available for basic education remain inadequate for the eligible number of children and youths."
UNICEF is a United Nations Program headquartered in New York City