Project-based science curricula can improve students' usable or meaningful understanding of the science content underlying a project. However, such curricula designed around "performances" wherein students design or make something do not always do this. We researched ways to design performance project-based science curricula (pPBSc) to better support the meaningful understanding of science content. Using existing curriculum design frameworks, we identified the learner's need to "create the demand" for the science content, anticipating how to use it in the performance, and to "apply" the science content, both being necessary to ensure meaningful understanding. Designing the pPBSc "I, Bio" we discovered how these guiding principles manifested as curriculum design challenges. We generalized from the design of "I, Bio" and related literature design approaches for addressing each challenge. Finally, we measured the extent to which a pPBSc incorporating these design approaches developed meaningful understanding. 652 middle grades students using "I, Bio" completed pre- and posttests on the science content behind the "I, Bio" performance. Our findings provide preliminary evidence that a pPBSc that incorporates these design approaches is consistent with gains in meaningful understanding. We discuss how the results of this work can be used to improve systematic experiments on instructional supports. (Contains 3 figures and 5 tables.)