In a study of seven southern African countries some primary teachers had only basic numeracy and literacy and actually scored lower than students in tests.
In half of African countries less than two-thirds of pupils complete five years of school, and these are often the countries with largest classes - sometimes one teacher for every 150 pupils.
Unesco's latest report on Education For All says 100 per cent enrolment is not enough, as poor teaching means many children drop out or leave without mastering the basics. In Malawi, for instance, primary school was made free in 1994 but the ensuing doubling of primary pupils by 2000 left schools struggling. Although 91 per cent of Malawi's 6 to 14-year-olds were enrolled, just 7 per cent had basic skills on leaving school.
Koichiro Matsuura, Unesco's director-general, said: "Overcrowded classes, poorly qualified teachers andill-equipped schools remainall too familiar pictures in many countries."