Computer science related topics are increasingly introduced at elementary school level, aiming not only to establish basic knowledge, but also to foster affective aspects such as motivation or self-efficacy. While corrective feedback is helpful to achieve the former, it may negatively impact the latter. This raises the question how to provide feedback in an encouraging way that makes learners feel competent but also autonomous. To shed light on this question, we conducted a robotics course with 45 children aged nine to eleven years, in which we studied their preferences when given a choice of either solving a problem themselves (with only a hint from the tutor) or being given the solution directly. We find that children like the freedom of choice and slightly prefer solving their problems themselves, which in turn is significantly correlated with a higher improvement in self-efficacy for building and programming robots. Interestingly, however, only girls exhibit a significant correlation with resulting knowledge on building, and only eleven year old children with resulting knowledge on programming. These insights allow us to provide concrete recommendations on how to give feedback and involve children and their preferences in elementary school computer science classes to promote both knowledge and self-efficacy.