## 4 Discussion
They summarized the broad ranges of dosage as follows: sessions longer than 20 min are not more effective than shorter ones, the median total number of sessions was 18, and the median duration was 42 days. [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) pointed out that vocabulary training targeted to a discrete set of skills (like in the present study, where we trained and evaluated a closed set of target words) might involve shorter-term intervention activities than those that are designed to enhance more global skills. More recently, [PERSON] et al. [PERSON] et al. (2018) reported a systematic review on the influence of dosage on the language outcomes of children with DLD. They could only include three studies looking at dosage and vocabulary training. [PERSON] et al. concluded that research is in its infancy and there is too much variation between studies in dosage, dose, outcome, outcome measures, and age of children to inform clinical practices [PERSON] et al. (2018). Concerning our measurement task, [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) used five different tasks to evaluate word learning. On the basis of their comprehensive assessment, they suggested that children with DLD have difficulties with both the phonological and semantic aspects of word learning. Our study could not provide such insights, as we chose to use only receptive vocabulary as the outcome. We chose to measure passive word knowledge, assuming that this would be a relatively easy task, since matching words to objects or concepts is one of the first steps in word learning (e.g., [37]). Furthermore, testing these young children with a word production task could have led to frustration when they would fail to name the pictures. In a picture-pointing task, a response can always be provided. Forced-choice, one-out-of-four picture selection tasks are frequently used to measure passive vocabulary in children (e.g., the standardized Peabody Picture Vocabulary Test, [38]). The follow-up results showed that at the end of the 5-week retention period, there was a significant growth in target words, although rather marginal, with a gain of approximately one extra word learned. No such gains were found for the control words, indicating that additional word learning did not take place for the untrained words. A positive point is that the newly learned words were still known at the follow-up. Another point for discussion is that we first analyzed the whole group of 70 children and then performed a secondary analysis with the 52 children who, according to the logbooks from the SLPs, completed all sessions according to the protocol. This secondary analysis yielded the same results. This finding strengthens our results, because it can be argued that the outcome of our study is more ecologically valid and fitting common practice, where therapy delivery can be suboptimal, as these young children are not always fit, fully concentrated, or cooperative. We did not use a highly experimental design where children have to learn novel words or receive intervention in a highly controlled clinical setting. All children received multidisciplinary group and individual therapy in special care daycare groups for children with DLD from 2 to 5 years old, and this the trial was embedded in their individual speech and language therapy. One might even argue that SLPs are unfamiliar with using tablet games as a relatively new medium, and hence the present results might be an underestimation of the real effect. For most of the children in our study, tablets were not a new medium; they were already familiar with tablets. Young children living in technology-based communities, such as the Netherlands, start using touch-screen tablets at an early age [39]. Young children are used to tablets and, according to [PERSON] [40], tablets may impact the emergent literacy of preschoolers and also have the potential for oral language development.