Young Minds Matter was the second Australian Child and Adolescent Survey of Mental Health and Wellbeing. Designing and conducting a national survey on a broad topic with widespread interest from many stakeholders was challenging. There were many key decisions to make along the way, such as deciding what topics to cover and how to measure them. With budget and respondent burden front of mind, it was necessary to stick to clear principles for selecting survey content and balancing priorities. It was a face-to-face survey, and we aimed for one hour in the house, including adolescents filling out their own survey in private. There were content casualties in the process, and on reflection, additional content that would have been valuable to include. Another key feature of the survey was linking survey responses with administrative data on Medicare-funded health care and with results from national standardized school achievement tests, providing a quasi-longitudinal lens. Developing a consent process that captured all these requirements, together with gaining approval from eight Education Departments in Australian States, proved to be very burdensome despite the benefits gained from these linkages. With data collection completed, another major decision-making point was how to determine prevalence of mental disorders, especially with a discord between parent and adolescent responses and various ways of determining impairment and severity. We discuss these challenges and others faced along the way as learning points for students looking to embark on population-level research, especially in mental health.