The Conservative government put out formal guidance on how to ban mobile phones in schools almost exactly a year ago. But 12 months later, a new study finds this approach does not have much of an effect on grades or mental health.

New evidence from the University of Birmingham has found students’ levels of sleep, exercise and academic record did not differ between schools with and without phone bans. The study also found restrictive phone policies did not lower the overall time young people spend on their phones each day. The research appears to contradict a study from last summer that found schools that effectively ban mobile phones see better GCSE results.

The research comes days after the education secretary branded a Conservative party proposal to ban phones in classrooms a “headline-grabbing gimmick”. Bridget Phillipson said she agreed that mobile phones should not be in lessons, but added the opposition was wrong to say it could only be done by introducing legislation