Modern teenagers are better behaved than their counterparts of 20 years ago, research suggests.
Boys and girls had "less problematic behaviour" involving sex, drugs and drink than teenagers surveyed in 1985.
However, girls in 2005 were likely to smoke and binge drink more than boys and start having sex earlier.
The researchers, Bournemouth University's Professor Colin Pritchard and Richard Williams, surveyed 10 schools along England's south coast.
In 2005 they repeated a 1985 survey of Year 10 and 11 secondary students and compared the results, published in the book Breaking the Cycle of Educational Alienation.
A 30-question survey was answered by pupils aged 14 and 15 and covered truancy, vandalism, theft, fighting, drinking and drugs, the same areas as the 1985 study.
Questions about sex, which were not permitted in 1985, were also included and compared with other research.
In 1985, about 824 pupils responded, with 854 answering it in 2005.
"The good news and, perhaps, unexpected is that the 2005 youngsters have less problematic behaviour than the 1985 cohort and even with the problematic behaviour, drugs, drink and sex, this is still a minority activity," said Prof Pritchard.
"The bad news, however, is that 20 years ago boys drugged, drank, smoked, truanted, stole, vandalised and fought more than girls.
"Today it is very different."
He said the girls smoked and drank "significantly" more than boys.
"They truant, steal and fight at similar rates to boys but have started under-aged sex earlier than boys - with 17% of lads in Year 11 having their first sexual intercourse (FSI) whereas 31% of Year 11 girls have had their FSI, indicating they are going with older boys," Prof Pritchard said.
Children of parents who smoke were four times more likely to start smoking themselves and twice as likely to steal, get into fights and become sexually active at an early age, the research showed.
Figures indicated they are also more than twice as likely to take drugs and/or binge drink.
"It is not that smoking causes the student's behaviour, but it reflects something of their personal, family and social relationships," said Prof Pritchard.