Work-based training has improved but almost half of courses are still below standard, a report says.
The provision of work-based training varied widely
The Adult Learning Inspectorate found 46% were inadequate in 2002-3, compared with 60% in 2001-2.
Its report said the large number of courses available - around 2,000 - was "confusing" would-be learners.
Some 40% of the organisations taking part were also poorly led, while many learners had not received the help they deserved, the report added.
Around 280,000 adults are currently in work-based learning.
The ALI's chief inspector, David Sherlock, described some providers as "not so much ill-managed as un-managed". Poor leadership and management blighted the sector.
Mr Sherlock added: "Disjointed systems, a confusing array of syllabuses, awards and awarding bodies make it very difficult for training providers to cut a clear path for their learners.
"Many of the shortcomings in leadership and management are made infinitely worse by the complicated design of learning programmes and awards."
'Should not be put off'
Mr Sherlock said: "Learning and training in the 21st Century should be of a high standard in order to support the economy as a whole.
"We need every single learner to succeed, whether it is as a plumber, a care worker in an old people's home or as an engineer.
"Nobody should have to suffer a poor experience and be put off learning for good."
He challenged the Learning and Skills Council, which oversees adult training, "to continue to be really tough with the very worst providers".
His report said the top five colleges were all sixth form colleges in which adult learners were in the minority.
In general, 16- to 18-year olds fares better in sixth form
colleges than they do in general further education
"The five best colleges are therefore not typical. Their good service to adults reflects very high standards available to all, rather than particularities of adult provision."
According to the Association of Colleges, the average amount of on-the-job training per employee in 2002 was only 1.8 days.
It stressed that the report was primarily not about college-based learning.
And it said: "Those colleges engaged in work-based learning report that one of the main problems they experience in delivering work-based learning is the reluctance of employers to fulfil their responsibilities to their trainees by, for example, offering them enough time off to complete their college courses or collect the evidence they need for their portfolios."
Among the good and outstanding work-based training providers, programmes in foundation studies, business administration, care and engineering featured most often.
'Too many courses'
Mr Sherlock said: "I challenge the government to insist on simplification in the sector, particularly when it comes to the unnecessary and confusing plethora of vocational and occupational qualifications.
"There are currently 2,000, where around 100 would do. "
From next January the ALI will introduce short monitoring inspections of providers that have performed poorly in the past and scraped through a re-inspection.
It is hoped this will reduce the possibility of "coasting".
Mr Sherlock said: "The process will not be bureaucratic but it will keep learning providers up to the mark and guarantee a decent service for learners. They are my priority."
The Skills and Vocational Education Minister, Ivan Lewis, said he was heartened by the improvement over the past year, but there was still much to be done.
The government had in place strategies to raise standards in the sector.
"Everyone must work together to make sure these improvements continue and can be seen in other parts of the sector such as adult and community learning, Learndirect and education in prisons.
"The real benefit of these advances in standards is high-quality programmes that deliver the successful outcomes our young people and employers need."