Training A: Group A (n1= 25 CNS+, n2 = 25 CNS-) will undergo working memory training program. The children will receive individual memory training based on the computer program Cogmed RM (Klingberg et al., 2005) and will be supervised by trained neuropsychologists. Its efficacy in the use with children with cancer has been recently published (e.g. Hardy et al., 2012). The children will undergo 25 training sessions "online"; each session takes about 45 minutes and consists of a selection of various tasks that target the different aspects of working memory. The difficulty level of the training is always adjusted based on the user's performance. The children will perform the memory training program at home over a period of 8 weeks. The child and a licensed Cogmed RM coach (neuropsychologist) will review and monitor the results of each day's training online. In an initial session at the Hospital (Zurich or Bern) the Cogmed RM coach plans and structures the training together with the child and the parents. The coach will provide weekly supervision and feedback on the child's performance and progress via phone call to the child's home. In the closing session with the child and the parents, the training experience will be reviewed .