Collaboration scripts have repeatedly been implemented in Computer-Supported Collaborative Learning (CSCL) to facilitate collaboration processes and individual learning. However, finding the right degree of structure is a subtle design task: scripts that are too rigid may impair self-regulation and hinder learning; scripts that are too flexible may fail to evoke high-level interactions. This study investigated whether making collaboration scripts adaptable would be a way to raise their effectiveness. Three experimental phases were realized: In a first phase (exposure phase), all students solved three problem cases by aid of a collaboration script in an asynchronous, text-based CSCL environment. In a second phase (treatment phase), another three cases were presented that were to be solved by aid of a different theory that was presented to the learners through a summary on a sheet of paper. During this phase, a three-groups between-subject design was realized: (a) an unscripted condition, in which students received no specific guidance how to structure their collaboration, (b) a non-adaptable script condition, in which students' collaboration was guided by the collaboration script they were trained in before, and (c) an adaptable script condition, in which students were allowed to modify parts of the trained script based on their self-perceived needs. In a third phase (subsequent transfer phase), students received a new case that they were to solve without guidance. N = 87 university students participated. Results showed that during the treatment phase, planning processes were most often performed in the unscripted condition. Yet, the adaptable script substantially increased students' engagement in metacognitive activities of planning compared to learning with a non-adaptable script, and increased monitoring and reflection activities when compared to learning without script. Mediation analyses showed that the adaptable script facilitated learners' use of self-regulation skills in the subsequent, unscripted transfer phase through the promotion of co-regulation processes of reflection in the treatment phase. The results reveal that adaptable scripting is a promising means of implementing flexible scripting and promoting self-regulation in CSCL.