Activation policies have increasingly targeted new and ‘hard‐to‐serve’ clients with complex needs, often deprived of the labour market experience, health, skills, and competencies that employers look for. The role of the health sector as a partner for welfare services has thus become more important. Cross‐sectoral frontline delivery of activation is seen as crucial in succeeding with activation and labour market integration in general and especially for young adults with complex needs. The current study aims at contributing new insights on such cross‐sectoral coordination by investigating how various actors within the welfare and health services experience interagency collaboration in the context of activating young welfare clients in the Norwegian Work Assessment Allowance scheme (WAA). Our data consist of 33 interviews with frontline workers in the two sectors in six different municipalities. Our data suggest that cross‐sectoral work in Norway directed at young WAA‐clients is hampered by a lack of coordination and communication between frontline workers in the two sectors, leading to tension and inefficiency in activating these young clients. We do, however, find that in‐house medical advisers in the welfare services have a potential to act as boundary spanners, but that seem to be an underused asset in this regard. We conclude that frontline workers' opportunities for cross‐sectoral coordination seem to be constrained by narrow and insufficient spaces for integration and collaboration, possibly due to organisational and administrative barriers.