And in rural areas of Wales, 78 per cent of schools have weak forms of governance, according to the report produced by Birmingham university for the Assembly government.
Governors are also not representative of the communities their schools serve. They tend to be white, middle-aged, middle-class, middle-income public service professionals and managers.
The under-representation of ethnic-minority parents and those from disadvantaged communities is a serious concern, say the report's authors.
But governors themselves feel dissatisfied with the situation. And they do not want more power or control going to heads or local education authorities.
The report's authors note that strong governance is closely associated with school improvement, with stronger governing bodies found in secondary schools and urban areas. They recommend more training for governors and help to strengthen their ability to scrutinise the work of their schools.
Governors Wales, which represents Wales's largest unpaid volunteer group of 26,000 people, called earlier this year for all new governors to undergo training.
The government has set aside an extra pound;200,000 for governor activities in 2006-7. An Assembly spokesperson said it had commissioned recruitment materials aimed at attracting people from ethnic minorities and the business world into school governance.
The findings were based on visits to 80 primary and secondary schools in 10 LEAs across Wales, carried out in 2001-2.
School governance and improvement in Wales, see www.learning.wales.gov.uk