Solving an open problem as proposed by inventing and productive failure approaches has been shown to prepare learners effectively for subsequent direct instruction even though invented solutions are often suboptimal for the given problems. Inventing can make the learners aware of knowledge gaps (cognitive) and more curious about and interested in the learning contents (motivational effects). However, working on the same problem with a given (optimal) solution helps avoid misconceptions and disorganized knowledge, while providing useful basic knowledge. Therefore, a given solution could be more effective. In an experiment (N = 42), we tested to what extent working on an open problem (inventing) versus a solution prepares student teachers for learning strategy evaluation. The inventing group invented criteria to evaluate learning strategies while the worked solution group studied the same problem in a solved, worked-out version. We found differential effects: inventing enhanced knowledge-gap experience, curiosity, and interest. However, studying the worked-out solution enhanced learning outcomes.