The aim of this study was to generate a substantive theory, based on interviews with children and adolescents with low back pain (LBP), explaining how they manage their main concerns in daily life. Tape-recorded open interviews were conducted with 14 boys and girls with LBP, aged 12-18 years, who participated in a 12-week physical therapy intervention. The grounded theory was used for analyzing the transcribed interviews. A core category, mobilizing own resources, emerged from the analysis, describing how adolescents with LBP succeed in managing their main concern, gaining body confidence, in daily life. The core category was divided into four categories labelled: coaching from the physiotherapist, seeking for information, compliance with physiotherapy and gaining energy from pain-free moments. The categories formed a substantive theory, illuminating how young people with LBP experienced physical therapy intervention. The theory explains and provides a deeper understanding of the main concerns of these adolescents and their strategies in managing their life situation.