While some pupils were benefiting, others were missing out, Ofsted said
Only half of school music lessons in England are good enough, according to inspectors from the watchdog Ofsted.
Its report said pupils were missing out on the positive impact music had on personal and academic development.
Lessons were judged to be "good" or "outstanding" in just half of the 84 primary and 95 secondary schools seen between September 2005 and July 2008.
The government said it was supporting councils to help them provide music education to all Key Stage 2 pupils.
Too many primary and secondary school children were not making as much progress in music as they should, despite their enthusiasm, said Ofsted's report, Making More of Music.
Standards were good or outstanding in 46 primary schools, satisfactory in 33 and inadequate in five.
Music provision was judged to be good or outstanding in just less than half of the 95 secondary schools and inadequate in 13.
Music teachers were generally found to be committed to the subject.
But they were often professionally isolated and lacked professional development and opportunities to discuss music. Many were unaware of recent initiatives.
The report welcomed government funding for music, but said it needed to be better targeted to have more impact.
Inspectors said the Training and Development Agency for Schools should provide continuing professional development and support for music teachers in secondary schools and subject leaders for music in primary schools.
And the Qualifications and Curriculum Authority should provide clear guidance on musical progression so that teachers could better plan for, teach, and assess music.
Local authorities and music services should make sure more children from different social groups benefited from playing a musical instrument.
And they said schools should regularly review their music provision.
Chief inspector Christine Gilbert said: "It is vital that subject leaders in primary schools and music staff in secondary schools enjoy good support and professional development, and that they have sufficient time, not only to monitor teaching and learning, but also to work with other teachers.
"More thought needs to be given to how very welcome national initiatives link to the music curriculum as a whole, how to ensure longer-term impact, and how to ensure that initiatives reach those most in need of help."
Schools Minister Sarah McCarthy-Fry said the government had made £332m available for music education from 2007 until 2011.
"We will work with members of the Music Programme Board to address the recommendations that Ofsted makes," she said.
"It is encouraging to see the positive effect whole class instrumental and singing programmes are having on music education generally.
"This is why we are supporting local authorities to provide these opportunities to all pupils at Key Stage 2 (approximately ages eight to 11)."
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Music, particularly group singing, is a great way to increase a child's cognitive skills
Chris Keates, general secretary of the NASUWT teachers' union, blamed the previous Conservative government for the problem.
"The decline in music provision has its roots in the previous government's vandalism of excellent local authority music services due to changes in education funding.
"This resulted in the demise of many central services, including music, on which schools relied for support and expertise."
Ms Keates said primary school league tables had also had a major part to play in a decline in music provision.
"The lack of priority given to music in schools is also a legacy of the school accountability regime," she said.
"This drives schools to prioritise those subjects whose results feed the performance league tables.
"This causes subjects such as music to be marginalised, which in turn affects the recruitment and retention of music specialists."