From the BBC:

Banning all unhealthy snacks in schools is the best way to get pupils to eat healthily, according to a study from Cardiff University.

The researchers found that peer pressure also had an impact on youngsters' healthy eating. They say the findings highlight the need for schools to put policies in place to back up healthy eating. But the National Association of Head Teachers (NAHT) said they do not back schemes imposing solutions on pupils. In a year-long study, researchers from the Cardiff Institute of Society, Health and Ethics looked at the snacking habits of nine to 11 year-olds at 43 primary schools in deprived areas of south Wales and south west England.

The research found that fruit tuck shops alone had a limited impact on how much fruit children ate at school. However, they had a much greater impact on schools which also had a "no food " or "fruit only policy".

 Link to full article on the BBC website

Moley's comment - Take away the option of the more attractive sweet snacks and only offer fruit. If a child is hungry, and there's no other option, they will tend to eat healthily. Seems a bit obvious really! Not the most ground-breaking research...but a good idea nonetheless.