The reference condition in this study involved a story-based vocabulary intervention delivered via videos of a speech and language therapist (SLT) reading stories. Target words (verbs and adjectives) were embedded incidentally in the narrative and presented four at a time. Frequency of word presentations was controlled across conditions to ensure comparable exposure. This condition represents an implicit, story-only approach against which experimental augmentations were compared.
In the explicit teaching experimental condition, the SLT delivered additional, structured instruction alongside the story-based presentations. Explicit teaching components included: providing definitions for target words, modelling the words in sentences, requesting retrieval from the child, and using a cueing hierarchy to support recall. These components aimed to increase intentional learning opportunities and strengthen semantic and expressive knowledge beyond incidental exposure.
The signing condition supplemented the story videos with augmentative signs for each target word. The delivering SLT signed the target words as they appeared in the story, integrating visual-gestural cues with spoken language. This augmentation maintained the same presentation frequency and story context as the reference condition, differing only in the concurrent use of signs to support word learning.
A fourth condition combined both sets of augmentations: explicit teaching elements plus augmentative signing alongside the story. As with other conditions, word presentation frequency was controlled and word sets were counterbalanced to reduce confounds. The combined condition tested whether the two putative active ingredients would produce additive or synergistic gains over either alone.
This was a within-participant randomized design involving 18 school-aged participants (age range 7;09–15;02 years). All participants had a language disorder: 14 were identified with developmental language disorder (DLD) and four had an associated biomedical condition. Over an 8-week intervention period, participants were taught 48 real verbs and adjectives that were randomly assigned to one of the four conditions. Word sets were counterbalanced across participants to minimise order and item effects.
Two primary outcome measures assessed vocabulary learning and use: (1) a word definition task to evaluate semantic knowledge, and (2) a sentence generation task to assess expressive use of taught words. The analysis employed Bayesian models to compare progress across conditions and to evaluate associations between participant characteristics (age, language ability) and intervention outcomes.
Participants demonstrated stronger progress in all three experimental conditions (explicit teaching, signing, combined) compared with the reference story-only condition. Bayesian analyses indicated that adding both explicit teaching and augmentative signing in combination did not lead to greater progress than adding just one of these components alone. In this sample, neither participant age nor baseline language ability was associated with the degree of intervention progress observed.
The study provides evidence that supplementing a story-based, incidental vocabulary intervention with either explicit teaching or augmentative signing can improve learning of verbs and adjectives for school-aged children with language disorders, including DLD. Importantly, the combination of both strategies did not yield additional benefit beyond either augmentation alone.
From a practical perspective, the findings suggest that clinicians and educational staff (speech and language therapists, teachers) can choose either approach to strengthen story-based vocabulary teaching. The authors note that signing may be quicker to implement in some settings because it can be delivered alongside speech, whereas explicit teaching requires additional targeted instructional steps (definitions, modelling, retrieval practice). Intervention choices could therefore be tailored to staff skills, time constraints, and child or classroom preferences.
The trial also underscores the importance of analysing active ingredients within interventions. Rather than assuming that adding more components will increase effectiveness, systematic comparison of individual and combined components can identify efficient approaches that produce meaningful gains without unnecessary complexity.
The study sample was small (N = 18) and included participants with a mix of DLD and associated biomedical conditions; the authors explicitly state that larger-scale studies are needed to explore differences between participants and experimental conditions more fully. Details such as longer-term maintenance, generalisation to classroom outcomes, and differential responses by participant subgroups were not reported in the abstract and require further investigation. Replication with larger samples and examination of potential moderators (for example, individual learning profiles or staff implementation fidelity) would strengthen guidance for clinical practice.
Within this controlled, within-participant study, adding either explicit teaching or augmentative signing to a story-based vocabulary intervention produced greater improvements in learning new verbs and adjectives compared with incidental story exposure alone. Combining explicit teaching and signing did not produce additive benefits. The findings support incorporating one of these strategies when delivering vocabulary intervention for children with (developmental) language disorder, while acknowledging the need for larger studies to refine recommendations and explore individual differences.