The survey didn't cover the conflict zones of the north and east, which include areas controlled by the Tamil Tigers.
Despite its modest national income and long-running war Sri Lanka scores highly on education performance.
It is placed seventh out of 104 developing countries.
Education has always been a priority in Sri Lanka.
The schools have remained open and attendance high, in spite of the 17-year-long war between the government and Tamil Tiger rebels.
A central bank survey carried out three years ago put the overall literacy rate at nearly 92%.
The survey didn't cover the conflict zones of the north and east, which include areas controlled by the Tamil Tigers.
While the Tigers are known to recruit young people, there's still an emphasis on education in their areas and schools have remained open.
They are also functioning in the government-held northern Jaffna peninsula despite the current fighting there.
Gender equality
School enrolment figures are evenly spread in all provinces, and literacy rates in the rural areas are almost as high as in the towns and cities.
One of the main areas where Sri Lanka has been praised is on gender equality, with nearly 90% of women being literate.
Experts say the introduction of free education for all encouraged families to send their girls to school, unlike other sub-Asian countries.
On an island where both the president and prime minister are women, there appears to be little culture bias against educating girls, although activists say they still choose arts and beauty subjects for further studies rather than engineering or computers.
The main problems are found among the workers in the sprawling tea estates, traditionally among the lowest-paid, where education was neglected for years.
Schools have now been established in the areas, but the literacy rate is still far below the national average and only two-thirds of female estate workers are literate.
One educationalist said Sri Lanka had established a tradition of sending children to school, but the challenge was now to educate the remaining 10% who still slip through the net.