But for a few enterprising teachers, the education system is rife with opportunities for personal financial gain.
A report on corruption in education, published this week by Unesco, the United Nations education organisation, highlights ways in which heads, teachers and education officials can extort and embezzle school funds.
Entry into the profession and progression up the salary scale offer considerable opportunities. In Liberia, six teachers were found guilty of buying the degrees that ensured their promotion. These false degrees had earned them almost pound;15,000 each in extra pay.
In Mexico, the National Education Workers Union set up a system of patronage, selling teaching positions for a price. Staff promotion became dependent on paying a bribe.
The greatest beneficiaries of corruption are usually headteachers. Many fill their school payrolls with teachers who are dead or retired. They are also able to manipulate school accounts. Some extort money from pupils for books, exam entrance and progression to the next class.
Others rob school funds for personal use. Colleen McCabe, the one-time nun and head of St John Rigby comprehensive in south London, used pound;500,000 of school money to finance a five-year spending spree.
The Unesco report claims that some teachers are "taking advantage of their professional relationship with students for private gain, including sexual favours". Some deliberately teach poorly in school in order to create a demand for private tuition.
But the NUT said that British teachers are unlikely to use the report as a lesson in illicit profiteering. A spokeswoman said: "Such creativity should be directed towards encouraging pupils to learn. If teachers here are desperate for additional cash, they tend to work in bars at the weekend."