To evaluate the effectiveness of a family-centred group education programme, in adolescents with Type 1 diabetes.Three hundred and five adolescents with Type 1 diabetes; age 13.1 ± 1.9 years, diabetes duration 5.6 ± 3.3 years, BMI 20.9 ± 3.7 kg/m(2) , HbA(1c) 78 ± 6 mmol/mol (9.3 ± 1.9%) were randomly allocated to the Families and Adolescents Communication and Teamwork Study (FACTS) diabetes education programme; (six 90-min monthly sessions attended by parents and adolescents incorporating skills training and family teamwork) or conventional clinical care. Primary outcome was HbA(1c) at 18 months (12 months post-intervention). Secondary outcomes were HbA(1c) at 9 months, psychosocial outcomes, adolescent quality of life, well-being, family responsibility and insulin dose adjustment behaviours at 12 months (6 months post-intervention) and episodes of severe hypoglycaemia and diabetic ketoacidois during the 12 months post-intervention. All analyses are intention to treat.Session attendance was poor with 48/158 families (30.4%) not attending any sessions and only 75/158 (47.5%) families attending ≥ 4 group education sessions. All biomedical and psychosocial outcomes were comparable between groups. At 18 months there was no significant difference in HbA(1c) in either group and no between-group differences over time: intervention group 75 mmol/mol (9.0%) to 78 mmol/mol (9.3%), control group 77 mmol/mol (9.2%) to 80 mmol/mol (9.5%). Adolescents perceived no changes in parental input at 12 months.Poor attendance of group education sessions delivered in routine clinics was a major challenge. More personalized educational approaches may be required to support and motivate families who are struggling to integrate the demands of intensive insulin regimens into their daily lives.