An economic downturn, years of fighting and little government support has left Iraq's school system lacking, UNICEF found in a new study of more than 20,000 families.

Socio-economic status creates a huge gap in who graduates from secondary school -- 73 percent for the wealthiest students compared to just 23 percent of the poorest students.

One-third of schools across the country operate multiple shifts in an effort to enrol as many kids as possible, meaning students may get just a few hours of class per day.

To improve access to education, Iraq needs 7,500 new schools, UNICEF said.

"It's to do with the conflict, the economic collapse, and lack of investment over the past 20 years. When the quality falls, then children themselves march out of the classroom," UNICEF country director Peter Hawkins told AFP.

"Children are the future of this country, and a growing gap between the 'haves' and the 'have-nots' sows discord and is detrimental for children and for Iraq," he added.

The wide-ranging study was the first in seven years in Iraq.

The country's infrastructure, including its schools, has been hit hard by conflict, from the US-led invasion in 2003 to years of sectarian violence and bombings.

In 2014, the Islamic State group overran a third of the country, implementing its own twisted curriculum in schools before being ousted from its urban strongholds last year.

And in recent months, a water crisis in the country's south kept many children at home in fear of contracting diseases.

To get more children in school, the government must boost its spending on education, one of the lowest rates in the region at just 5.7 percent of total expenditure, UNICEF said.

"Ministers: please use this to target investment to those children in greater need. Those children are your future," Hawkins urged government members.

Parliamentary divisions mean Iraq has not appointed anyone to head the ministries of education or higher education.

According to Iraq's Human Rights Commission, more than 1,050 schools across the country have been damaged to varying degrees by the recent violent years.

Sixty percent of the country's 39 million people are under the age of 24.