This article reports on research using data from the second Australian Child and Adolescent Survey of Mental Health and Wellbeing to investigate the relationship between mental health disorders and performance on NAPLAN. Mental health disorders were common, with one in seven students affected, with males more likely to be affected. Students with mental health disorders had more absences from school than their peers without a disorder. Over time, students with mental health disorders fall increasingly behind their peers so that by the time they complete their final NAPLAN test in year 9 they are almost three years behind their peers. Students with mental disorders also had higher rates of self-harm. The authors concluded that while the availability and use of services for children with mental health disorders and their families has improved, there are still many children and families who do not receive needed support.