Our research conducted two iterations of a mixed methods design-based research project with 87 youths, to improve learners' collaboration and knowledge-building by using collaboration scripts during learning-on-the-move within a mobile computing intervention. We investigated how the informal mobile augmented reality app influenced children's science knowledge related to tree life cycles and how the mobile learning intervention shaped children's collaborative sense-making, which involved coordinating sensory observations with explanations as they walked through forested areas of a nature center. Iteration A included four scripts to support collaborative sense-making and knowledge-building, and Iteration B included two additional scripts to support learning regulation. Our results showed significant, large gains in science content scores between pre- and post-assessment for the children in both iterations; however, no difference in learners' knowledge gain was found when comparing Iterations A and B. We qualitatively coded video-records of 39 small groups to understand children's sense-making related to observational and explanation practices. Iteration B groups, who were provided with two additional collaboration scripts, were better able to engage in collaborative sense-making and peer negotiation as they coordinated observational evidence with explanations of tree life cycle stages. Study implications include when designing out-of-school-time experiences, collaboration scripts can guide complex scientific sense-making that includes observation and explanation when children are learning-on-the-move.