Morphosyntactic problems are a core symptom of Developmental Language Disorder (DLD). In the Netherlands, children with (presumed) DLD can receive special care in language-focused treatment groups. The focus of these groups mainly lies in improving communicative intentions, vocabulary and phonology. Morphosyntactic skills receive less attention. The authors developed a scripted group-based intervention targeting morphosyntactic skills in young children with DLD. In this study, the effect of the intervention on the morphosyntactic skills of preschoolers with (presumed) DLD was tested and the usability for pedagogical practitioners (PPs) was evaluated. Twenty-seven preschoolers with DLD (aged 2;10-3;10 [years;months]) participated in an A-B group study in which the development of grammatical structures was monitored with a morphosyntactic task and language sample analyses (LSA). Progression during 8 weeks usual care (UC) and 8 weeks morphosyntactic intervention was examined using Bayesian mixed effects models. In LSA, structures that were targeted were compared to control structures. The intervention consisted of a weekly script-based group session in which morphosyntactic structures were targeted, and daily activities in which these target structures were repeated. The intervention was provided by trained PPs, who were coached by a speech-language therapist. An early indication of usability and feasibility was evaluated using an online questionnaire. The analyses show that morphosyntactic skills improved during the intervention period, with strong evidence for growth in the production of target structures on the morphosyntactic task and target and control structures in LSA, while barely any evidence was found for growth in the use of these structures in UC. However, target structures and control structures seem to develop at the same rate. General measures of morphosyntactic ability showed improvement both during UC and the intervention phase. Evaluation among practitioners suggested that the intervention is regarded as usable and feasible. Growth in morphosyntactic skills of children in the intervention period was demonstrated, but this could not be proven to be related to the intervention because both target and control structures improved during the intervention. This growth might be due to maturation instead of the intervention. Nevertheless, our study demonstrates that the morphosyntactic skills of preschoolers with DLD can show considerable improvement over a period of 8 weeks. Furthermore, our study underlines the importance of using LSA measures when monitoring the morphosyntactic development of children, as they might be more sensitive to change than standardised tests. What is already known on the subject Most children with Developmental Language Disorder (DLD) experience difficulties in their morphosyntactic development. In the Netherlands, preschoolers with DLD can receive special care in language-focused treatment groups. These groups mainly focus on stimulating communicative intentions, vocabulary and phonology, but less so on stimulating morphosyntactic skills. What this study adds We designed a new group-based intervention targeting the expressive morphosyntactic skills of children with DLD, examined the effect and investigated the usability and feasibility. Although there is strong evidence for growth in morphological skills, intervention effects could not be demonstrated. Evaluations among practitioners suggested that the intervention is regarded as usable and feasible. Furthermore, this study shows that children's morphosyntactic skills can improve over relatively short periods of time and language sample analyses seem to be sensitive to detect these changes. What are the clinical implications of this work? Currently, very few group-based morphosyntactic interventions exist (in the Netherlands). Since practitioners were generally positive about the intervention and its usability and feasibility, the proposed intervention might benefit the treatment of morphosyntactic problems in children with DLD.