Purpose: Applying evidence-based grammar intervention can be challenging for speech and language therapists (SLTs). Language in Interaction Therapy (LIT) is a focused stimulation intervention for children with weak morphosyntactic skills, which was developed to support SLTs in incorporating results from effect studies in daily practice. The aims of this Clinical Focus are (a) to explain the principles and elements of LIT and stimulate use in daily SLT practice and (b) to describe the effects of LIT on morphosyntactic skills of 4- to 5-year-olds in special education, compared to usual care.

Method: With a description of LIT, we provide guidance to implement evidence-based intervention. Important elements are as follows: proper selection of therapy goals, language facilitating techniques, child-centered and clinician-directed elements, and the use of scripts. Our focus in the description is on the support and practical solutions LIT tries to provide to SLTs. We also explored the implementation of LIT in special education, to improve morphosyntax in 4- and 5-year-old children. We provided SLTs with training and designed protocols for each therapy session. The effects of LIT were measured in a single-case A-B design, repeated in five children with developmental language disorders (ages 4;2-5;7 [years;months]).

Conclusion: We conclude that implementation of LIT is possible if LIT is enriched with support in goal selection, protocols to guide therapy sessions, and training and coaching. In the single-case study, four children showed more growth in mean length of utterance during and directly following the LIT intervention phase, compared to the baseline phase with usual care, and in two of them, this difference was significant. The grammatical complexity measure "TARSP-P" showed an overall significantly higher score at group level during LIT, but limited effects on an individual level.