Previously, a total of 121 children with an autism spectrum disorder (ASD) performed an adaptive working memory (WM)-training, an adaptive flexibility-training, or a non-adaptive control (mock)-training. Despite overall improvement, there were minor differences between the adaptive and mock-training conditions. Moreover, dropout was relatively high (26%). In the current study we explored potential predicting and moderating factors to clarify these findings. The effects of intelligence, autism traits, WM, flexibility, reward sensitivity and Theory of Mind on dropout, improvement during training, and improvement in everyday executive functioning (EF), ASD-like behavior, and Quality of Life (QoL) were studied. None of the predictors influenced dropout or training improvement. However, 1) more pre-training autism traits related to less improvement in EF and QoL, and 2) higher reward sensitivity was related to more improvement in QoL and ASD-like behavior. These findings suggest that these EF-training procedures may be beneficial for children with fewer autism traits and higher reward sensitivity. However, the exploratory nature of the analyses warrant further research before applying the findings clinically.