Deficits in working memory (WM) have been reported repeatedly in children with primary language impairment (PLI) and may significantly contribute to the language difficulties that are experienced by these children. However, interventional studies within the field regarding the cross-domain effects between working memory and language are limited, and their results are contradictory. Therefore, the first aim of this study was to explore whether WM training can improve the WM skills of these children and whether the effects of training could be transferred to language, specifically to grammatical skills. The second aim of this study was to investigate the near and far transfer effects of direct language intervention on grammar and WM, respectively, as this is the most (and sometimes the only) considered treatment programme for children with PLI. Using a single-subject experimental design, ten 6-8-year-old children with PLI received WM training and language intervention, respectively, in two consecutive phases of study. The treatment gains on targeted areas and generalization to the other domain were tracked by repeated measurements of some WM and language tasks and were completed by a set of pre- and post-intervention measures. Regarding the results, it appears that if sufficient time is spent on WM training, WM-related skills improve and the effects also transferred to morpho-syntactic language skills. However, a cross-domain effect in the reverse direction is questionable. Though the language intervention programme resulted in good gains in grammatical skills, it did not improve participant performance in WM tasks, with the exception of non-word repetition (NWR). The observed participant gains in non-word repetition were likely due to the improvement in higher-level linguistic processing, rather than the actual enhancement of WM skills.