Transfer motivation is an important factor influencing transfer of training. However, earlier research often did not investigate transfer motivation as a multidimensional construct. The unified model of task-specific motivation (UMTM) takes into account that (transfer) motivation is multidimensional by including both affective and cognitive motivational components and their antecedents. Prior research has provided evidence that the UMTM can predict self-reported transfer of training, but is unclear whether it also can predict transfer reported by expert external raters. Moreover, it is unclear whether controlling for prior knowledge matters for the relationship between transfer motivation and transfer of training. This study improves on existing research by accounting for both of these gaps in the literature. Data were collected among 299 participants who filled in a questionnaire about the UMTM components directly after attending a writing training. They also handed in written documents before, and 6 weeks after the training, which were rated on transfer by trainers. Outcomes showed that components of the UMTM positively predict externally reported transfer when prior knowledge was controlled for. The outcomes imply that the UMTM has predictive value for transfer of training and points out which factors influence whether transfer does or does not occur.