Schools in England should do more to teach children about the dangers of drugs, tobacco and alcohol, the education watchdog Ofsted has warned.
Drugs education was 'mixed' across England, inspectors found
There was a "very mixed picture" across the country, with too little emphasis on the mental health problems linked to substance abuse, inspectors found.
But government efforts to promote exercise and good eating in schools were having a "positive impact".
Ofsted visited 18 schools which had been praised for good health practice.
In 13, pupils were taught how to make healthy lifestyle choices, but a minority did not focus enough on drink, drugs and smoking.
Ofsted also looked at previous data gathered from inspections at 102 other schools.
Here, there was "too little focus on the social implications of drug-taking", inspectors found.
Ofsted's survey - Healthy Schools, Healthy Children? - also suggested the quality of food served in schools varied widely.
In those where meals were prepared elsewhere and brought in, there was "continuing poor nutritional value".
But in schools where parents were included in establishing a healthy-eating policy, standards were high.
In one primary, lunches were labelled with differently coloured flags to encourage pupils to follow a balanced diet.
In one secondary, the chef had remodelled the canteen on high-street restaurants in an effort to attract children.
Ofsted's director of inspection, Miriam Rosen, said: "The majority of schools are making a valuable contribution to pupils' health and wellbeing.
"Now is the time for the government to focus on those schools that are not making such a positive contribution."
The report said three of the 18 schools surveyed "took too limited a view of their responsibilities to provide sex and relationship education and support for pupils' emotional development.
"Resources and teaching strategies were narrow and focused on physical changes, and staff lacked confidence and expertise in dealing with aspects of sex and relationship and drug education."
Some schools did not do enough to encourage exercise. In two secondary schools, lunchtimes were "too short" for sport to be played effectively.
Pupils were sometimes discouraged from cycling into school, which had a "negative impact" on physical activity.