BACKGROUND: Adolescence is a period of profound developmental change during which the prevalence of mental health problems starts to increase. It also typically coincides with a school transition. Understanding mental health trajectories through school transition is important to inform interventions to support young people's mental health during this period. METHODS: In a longitudinal study with three assessment points spaced six months apart spanning the transition from primary (T1 = end of primary school [Year 6]) to secondary school (T2 = beginning of the first year secondary school [Year 7]
T3 = end of first year of secondary school [Year 7]) we carried out a latent class growth analysis of symptoms of common mental health problems. Young people (mean age at baseline of 11.2 years, standard deviation 0.29
46.8% female
53.2% male) from South East England ( RESULTS: A model with four trajectory classes provided the best fit to the data: 'persistently elevated' mental health problems, 'emotional and peer problems', 'hyperactivity and conduct problems' and 'persistently low' mental health problems. Class membership was differentially predicted by the individual-level variables. CONCLUSIONS: Young people from low SES backgrounds, those with SEN and those who have experienced two or more NLEs are more likely to exhibit trajectories with elevated mental health difficulties through the transition to secondary school. Young people who were worried about transition were more likely to belong to a trajectory class characterised by elevated emotional problems.