External representations can be powerful to support learners' collaborative knowledge construction. They can focus learners on aspects which are particularly important for the task to solve. In this study, we investigate different styles of pre-structuring shared external representations, a collaboration script and a content scheme. 159 university students participated in the empirical study. They were assigned randomly in groups of three to one of four conditions in a 2x2-factorial design with the factors of collaboration script and content scheme. Results show that learners benefit particularly from the content scheme. The scheme was able to influence learners' spoken discourse and focused it on aspects necessary for the task solution. Furthermore, also learners' collaboration outcomes benefit from the content scheme.