We apply the notion of 'semantic waves' from Legitimation Code Theory (LCT), a powerful educational framework, to Computer Science Education. We consider two case studies exploring how a simple analysis can help improve learning activities. The case studies focus on unplugged activities used in the context of both teaching school students and teacher continuing professional development. We used a simple method based on LCT to analyse the activities in terms of their 'semantic profiles': changes in the context-dependence and complexity of the knowledge being taught. This led to improvements to the activities. We argue that 'semantic waves', or moves back and forth between concrete/simpler and abstract/complex knowledge, help show ways that an unplugged activity might be effective or not, and how small changes to the activities can make a difference in potentially offering a more fruitful learning experience.