Think about activity levels. I bet weekends are more sedentary than week days? During the week when I am at work (8-8 most days) my BG levels rarely go above 8, whereas if I have a casual wknd I can sometimes get to double figs. Also pay attention to when eating and how much. So, for example a packed lunch usually will have less food in it compared to having access to food cupboards in the kitchen etc.
Try doing a wknd where you go on a bike ride together, or to the swimming pool and I bet the BG levels will be more acceptable.