"Groups of over 26 are not uncommon and 35 per cent are more than 20, usually in rooms designed for 20 pupils.
"In these situations teachers find it difficult to resource lessons adequately, or provide opportunities for sufficient practical work. Sometimes, they are rightly worried for pupils' safety," the inspectors add.
In primary schools, low standards and pupils' failure to progress in design and technology were often linked with "poor and cramped accommodation, large class sizes, and insufficient resources to enable pupils to have a sufficiently broad range of experiences" as well as teachers' lack of subject knowledge.
Many secondary school departments are "not able to resource the breadth and depth of activities needed for the national curriculum", says the report.
In addition, the gap between the best and worst provision of equipment is widening, ranging from capitation levels of less than Pounds 1 to more than Pounds 18. "Examples were seen of expensive new equipment lying idle because there was not enough money to buy the necessary consumable materials." Pupils often purchased materials and components for their own projects.
The report continues: "Given the constraints on funding, many schools do not consider books to be a high priority for spending within design and technology." Many books were outdated.
Steve Cushing of the National Design and Technology Education Foundation said technology was an expensive subject. "Class sizes in secondary schools have been growing and it does raise a lot of safety issues," he said.
Whether the resourcing problems were because of local management of schools funding or the requirements of the national curriculum - which brought in technology as a new compulsory subject in many places - was unclear.
The inspectorate report says most secondary schools have enough design and technology rooms to meet the demands of the subject, which has only been mandatory for all of key stage 3 since 1993. "However, most need enhanced provision in some way in order to meet the new demands of the subject." This year, some schools have been unable to fulfil their statutory requirements in Year 10.
Pupils beginning their GCSE courses in 1993-94 were the first who had to study technology. It has since been suspended for all other key stage 4 pupils until 1996.
Technology has been a particularly problematic national curriculum subject, and the 1992 decision to rewrite the much criticised original 1989 Order meant that many schools, under pressure from curriculum overload and testing, did not try to implement it fully. The new, slimmer version which emerged from the Dearing review will take effect in September for key stages 1, 2 and 3 and a year later for key stage 4.
It was "an important subject brought in at the wrong time for its own sake", said a School Curriculum and Assessment Authority spokeswoman.
* The Department for Education will be sending a new guide, Design and Technology: characteristics of good practice in secondary schools to all secondary schools in England. The booklet, written by the Office for Standards in Education and drawing on good practice seen in 300 schools, will be published by HMSO, price Pounds 9.95.