## 4 Discussion  
Our aim was to examine whether vocabulary intervention with tablet games was equally as effective as a standard intervention with traditional play material. Both in the total participant group of 70 children and in the smaller group of 52 children, who received  
Figure 3: Target words and control words at baseline (T0), directly post-intervention (T1), and at retention measurement (T2). the intervention exactly as photocolled, this was indeed the case. Three-year-old children with DLD learned as many new words in the tablet game condition as in the real objects condition. Our findings support the results from a prior study by [PERSON] and [PERSON] [PERSON] and [PERSON] (2018), where only target words were used without the addition of control words to evaluate the influence of incidental word learning. In our study, more target words than control words were learned in both intervention conditions, meaning that the children learned more new words during intervention than could be accounted for by natural vocabulary growth. In a similar vein, when comparing traditional therapy with an interactive computer game, [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) found no difference in gains for phonological therapy between these two conditions. In our study, contrary to other studies that tested the efficacy of computer tasks played individually by the child, the tablet game was played together with the SLP, who used similar prompting and language-stimulating techniques as in the symbolic play sessions with real objects. For our study, we developed a manual, 'Playing tablet games together', based on video analysis of therapy sessions with real objects and with games and a qualitative analysis of focus group discussions with SLPs [PERSON] and [PERSON] (2018). The latter analysis revealed that the most important difference between the study conditions was that more direction from the SLP and rules for turn-taking were needed when using tablet games. Otherwise, the children tended to hold the tablet and play the game on their own. This behavior is probably what they are used to doing in other settings, such as the home environment, where children play with their tablets independently. The SLPs mentioned that children liked to play the game together and discover the possibilities and hidden surprises. With regard to the gains found in our study, our study shows that vocabulary intervention is effective. However, the magnitude of this effect was somewhat disappointing. On average, the children learned 6 new words (receptively) in 12 10-min sessions. Clearly, for many children with DLD, expanding their vocabulary is challenging. This result corroborates [PERSON] et al. [PERSON] et al. (2018), who found that preschool children with DLD were poorer at learning new words than children matched either by chronological age or by mean length of utterance (MLU). Although the children in our study were exposed to the target words multiple times during the intervention period, this apparently was not enough to acquire all the presented target words. It might be that the children needed more time to learn to match the target words to objects or concepts. The dosage of our 2 vocabulary interventions was 10 min in 12 sessions in 8-9 weeks (56-63 days). We chose this frequency and duration since it resembled the usual Dutch care and intensity of interventions mentioned in previous studies. A large survey across Europe revealed that the predominant frequency of therapy for children with DLD is 1 session a week for 30-45 min [PERSON] et al. (2018). A therapy session usually contains different activities addressing various aspects of language, such as vocabulary, communication, speech sound production, and sentence comprehension. Our choice of therapy intensity was also informed by the outcomes of the meta-analysis of [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) on the effects of vocabulary intervention on language development of preschool- and kindergarten-aged children.