Corruption in education is a serious blight that undermines the quality and availability of schools and universities around the world, according to an international report.
Anti-corruption campaigners Transparency International have published a global survey showing that about one in six students has had to pay a bribe for education services.
In parts of sub-Saharan Africa and Asia this might be requiring parents to pay a fee for a school place that should be free.
In Eastern Europe, it might be paying to gain an advantage in university admissions.
The Berlin-based campaign group is best known for its annual "global corruption barometer", which measures levels of dishonest payments in more than 100 countries, based on more than 114,000 household interviews.
This year's survey also asked questions about people's first-hand experiences and perceptions of dishonesty in education.
In some countries these perceptions are distinctively negative. The report says that almost three-quarters of people in Cameroon and Russia see their education systems as "corrupt or highly corrupt".
The findings show a huge range of malpractice.
In Pakistan, there are warnings of thousands of "shadow schools" without any real students, but drawing public funding to pay for "ghost teachers".
"Leakages" in the funding of schools in Kenya had the equivalent value of losing more than 11 million text books, says the report. A study of 180 schools in Tanzania showed that more than a third of intended funds had failed to reach the school.
In Greece there are warnings about nepotism in jobs and promotions in higher education.
In Vietnam there is a problem with bribery for places in the most sought-after schools.
The report quotes figures from the United Nations showing 110 countries where fees are levied, despite in theory having free education enshrined in law. The report describes "myriad pretexts" to impose charges on parents.
Degrees of dishonesty
So why should education be so vulnerable to corruption?
Parents want the best for their children, says the report, and they can be exploited by unscrupulous officials controlling access to places.
It also involves a great deal of public money filtering down from central government to local school authorities. In Nigeria, the report says, $21m (£13m) intended for schools was lost in two years.
But it's not only a problem for the developing world or those providing the basics of schooling.
The massive expansion in demand for university education has created rich opportunities for illicit charges.
Students need degree-level qualifications more than ever and are under great pressure to get university places and to leave with good grades, opening up fertile territory for corruption and cheating.
Eastern European and former Soviet states are highlighted as having had particular difficulties.
In Georgia, there have been reforms to stop corruption in university admissions. This hadn't simply been "cash-filled envelopes", but included a complex system of having to buy tutoring, Transparency International found.
There could also be more practical types of illicit charges, with suggestions that in Romania access to university accommodation depended on bribery.
The demand for qualifications has also generated its own industry in fake universities.
In the United States, the report estimates, there are about a thousand "degree mills" in operation, selling bogus qualifications.
This isn't only harmless self-delusion, says the report, as these bought qualifications are used to gain graduate jobs, including in one case working in a nuclear power plant.
It also highlights the case of Colby Nolan, a student who ostensibly gained an MBA degree in 2004, until his owner revealed that the graduate was a six-year-old cat. He had gained the equivalent of an upper second class degree.
The growth of higher education as a globalised, multi-billion dollar business has also spawned a parallel opportunity for fraud, says Philip Altbach, director of the Center for International Higher Education in the Lynch School of Education at Boston College.
He has described the "spectre of corruption haunting" the move towards a more internationalised higher education system.
And he has called for more co-ordinated international efforts to set standards and share information.
The Transparency International study says that corruption has a corrosive effect on education, raising the cost and lowering the quality.
"Many people wouldn't realise the extent of corruption in education, right through from the financing of education through to academic corruption," says report editor, Gareth Sweeney.
"In some countries it's such a serious problem that it could undermine the credibility of their education systems."
There is some good news as the report highlights efforts to tackle bribery.
In Chile, anti-corruption lessons have been introduced to the school curriculum and in Bangladesh there is an "integrity pledge" taken by officials.
The proliferation of mobile phones in Africa is being used to allow people to expose concerns about bribery in schools.
Legal advice centres have also been developed in a number of countries to help community groups make legal challenges against school corruption.
There are also international efforts to improve the monitoring and tracking of education funds.
But corruption is still there leaching away education budgets. It's a particularly bleak problem when there are still tens of millions of children without any access to school.
"Corruption is an obstacle to a fundamental human right to education," says Mr Sweeney.
While there are campaigners calling for education for all, such as Malala Yousafzai in Pakistan, this report also warns of the barriers being created for the poorest communities by demands for corrupt payments.
Teachers take bribes to offset poor wages or irregular payments and that in turn raises questions about the lack of funding coming from higher up the chain.
Mr Sweeney says that there should be a way of measuring good governance in any future global education targets.
"Even when formal school fees are abolished, many households are still being forced to pay informal fees. How is a family supposed to be able to afford these costs, when they cannot afford their daily meals?," says Pauline Rose, director of Unesco's Global Monitoring Report, which tracks progress towards primary education for all.
"Until these hidden costs are eradicated, we will not be able to call education free, and universal primary education will continue to remain a distant goal for the poorest."