Starting school young is an exciting but sometimes challenging milestone for children and their families. Some children will be nearing their fifth birthday as they enter foundation classes while others will be only just four.
The study, led by the University of Exeter Medical School which investigated more than 2,000 children across 80 primary schools in Devon, has found that children who are younger than their peers when they start school are more likely to develop poorer mental health, as rated by parents and teachers.
A higher score a measure of poor mental health would indicate that children are more likely to experience common negative emotions such as worry and fear, they may have poorer relationships with their peers and be more likely to encounter issues with behaviour and concentration.
Overall the effect was small, however researchers believe the additional stress of keeping up with older peers could prove a "tipping point" for vulnerable children, such as those with learning difficulties or who were born prematurely.
The research team was supported by the National Institute for Health Research Public Health Research Programme and the Collaboration for Leadership in Applied Health Research and Care South West Peninsula (NIHR PenCLAHRC).
The research could have implications on parents' decisions on whether to defer their child's school entry for a school year, permissible under guidance introduced in 2014.
The findings could also influence how teachers interact with younger children, particularly those with additional complex needs in the class, and on assessments and teaching and support structures within classrooms.
Anna Price, of the University of Exeter Medical School, was motivated to study the issue after home schooling her own April-born son, who has pre-existing learning difficulties, and was not ready to start school aged five.
She said: "Using such a large dataset was a chance to explore what's really happening in practice for children who start school at a young age. We found that children who started younger had slightly worse well-being- however, this effect was very small and unlikely to make a difference for most.
The challenge to well-being of being young for your school year might however be one struggle too many for children who face other challenges to their mental health. Our findings can help guide parents and teachers in making decisions that best support the child."
The researchers also explored the impact of starting school early on the child's happiness levels and behaviour. In contrast to previous research, they found no significant impact on either. The research paper noted that the schools in the study had strong support in place, such as small group learning, which may have helped improve happiness and behaviour overall.
Professor Tamsin Ford, of the University of Exeter Medical School, oversaw the research. Professor Ford, a practising child psychiatrist, said: "Being relatively younger could be the tipping point for some, but certainly not all, children. For most it would just be something for teacher's to be aware of but for children with other needs or who were born prematurely this difference could be significant. Awareness of this issue among teachers and educators means measures can be put in place that could help to mitigate this effect and get the best outcome for children."
The study has been published in the journal Child Care, Health and Development.
