Citizenship is compulsory in the English curriculum
Some schools in England are struggling to cover citizenship properly, according to inspectors.
A report by Ofsted says that in some secondary schools, pupils have "important gaps" in their knowledge.
However, inspectors say lessons have improved since they were made compulsory seven years ago.
Their report, based on 91 schools, says just over half were at least "good" on the subject, but only one was rated "outstanding" and 10 were "inadequate".
In some of these cases, inspectors say, citizenship has been "misunderstood or ignored".
The study adds that in schools where citizenship lessons were only "satisfactory", students were getting an uneven education.
In some secondaries, pupils' knowledge was patchy, it says.
"Typically, students knew a good deal about some aspects of the curriculum (such as human rights), but had important gaps in their knowledge.
"The quality of teaching was also uneven and the curriculum only partly covered."
Often citizenship shared a timetable slot with Personal, Social, Health and Economic (PSHE) education, but the time allowed was "too little to do justice to either subject", inspectors say.
Inspectors praised schools which gave pupils opportunities outside the classroom - for example through volunteering or being part of a school council.
Ofsted chief inspector Christine Gilbert, said: "Citizenship is becoming a well established part of the school curriculum and this report highlights the ways in which schools are successfully promoting social responsibility, community involvement and political understanding.
"It is important that the good practice featured in the report is replicated more widely."
The government has accepted the report's findings in full and says it will maintain the number of initial teacher training places for the subject and continue to provide extra training for existing teachers.
Schools minister Diana Johnson said the report acknowledged the "real progress" which had been made over the past three years.
"We are pleased with the progress that has been made in getting Citizenship increasingly embedded in secondary schools and especially in primary schools where citizenship will become a statutory part of the curriculum next year," she said.
"But we do nevertheless take very seriously that some schools have more to do."