The study is a parallel cluster randomized controlled trial with therapy practices as clusters. After written consent from the patients, the therapists are randomly assigned to treat either the intervention or the control group. Blinded external assessors evaluate the patients using standardized outcome measures before and after the intervention, and six months later. The two coprimary endpoint assessments of arm and hand function as prerequisites for participation (defined as equal involvement in activities of daily living) are quality of arm and hand use and arm and hand function. Assessments are made four weeks post-treatment and relativized to baseline performance. Changes in primary outcomes are analyzed with mixed models, which consider the hierarchical structure of the data, adjusted to the baseline measurements and sex. The primary analysis compares the two randomized groups, with respect to the adjusted averages for each of the two coprimary endpoints. To keep an overall significance level of 5%, the two endpoints are tested at the significance level of 5% each in hierarchical order.