A £1bn programme of British aid for education in three east African countries has failed to teach basic reading, writing and maths skills to most of the children involved, an independent report found on Friday.
The report warned that "inadequate" attention was paid to the quality of education provided by the schemes in Rwanda, Ethiopia and Tanzania, and urged the Department for International Development (DFID) to revise its strategy to focus on results, rather than numbers.
The 10-year programme - due to run from 2005-15 - has succeeded in boosting attendance at schools "substantially".
However, the quality of education provided is "so low that a large majority is failing to achieve basic literacy and numeracy", said the Independent Commission for Aid Impact.
ICAI gave the programme an "amber/red" rating, meaning "significant improvements should be made".
International Development Secretary Andrew Mitchell accepted that there had not been enough emphasis on teaching quality, but said the Government had already taken action by launching pilots of "payment for results" schemes in all three countries.
Mitchell said the coalition Government set up ICAI in 2011 "to shine a light on development spending", adding: "We will use their findings to further improve the way we deliver aid around the world."
Friday's report found: "DFID has focussed on expanding access to basic education and has succeeded in boosting enrolment substantially.
"There has, however, been a lack of attention to learning outcomes and to the trade-off between increasing access and ensuring quality.
"As a result, the quality of education being provided to most children is so low that a large majority is failing to achieve basic literacy and numeracy.
"We are pleased to note DFID's new commitment to improving education outcomes but its recent strategies and approaches will need considerable improvement to rise to this challenge."
It added: "DFID's programmes have, until recently, given inadequate attention to the quality of education, including basic factors affecting pupils' opportunity to learn. These include pupil attendance and teacher effectiveness: both are key determinants of learning outcomes and value for money."
ICAI gave DFID a better rating for health and education programmes in the Indian state of Bihar, where it has made a "positive contribution" to improvements in learning achievements and a reduction in the infant mortality rate.
It said the practice of giving around 15% of the UK's bilateral aid budget - £643 million in 2010/11 - direct to recipient governments through so-called "budget support operations" had been "effective", though its practical value varies from country to country.
Chief commissioner Graham Ward said: "These reports show that some of DFID's work is having a real impact on the lives of the poorest people, particularly in India, which has seen considerable improvements in health and education.
"They also show, however, that there is more to do to get the most out of budget support and to make sure that education programmes in East Africa build on progress in enrolment to focus on ensuring a good education."
Mitchell said: "In the past there has been too much emphasis on just getting children through the door and not enough on quality. The coalition Government is addressing this with our pilots on 'payment for results' for education in Ethiopia, Rwanda and Tanzania.
"We are clear that it is not enough to simply have children sitting in a classroom - the quality of learning is what provides value for the British taxpayer, developing country economies and the children themselves."
Oxfam senior policy adviser Claire Godfrey said: "We are pleased that UK aid to East Africa has given more children the chance to go to school, but putting bums on seats is not enough and DFID needs to act urgently to raise standards."