Introductory physics labs are promising spaces for students to develop their abilities to creatively and independently solve research problems. However, many introductory labs focus their efforts on using experiments to demonstrate concepts from lecture, sacrificing student agency to ensure that lab activities can be carried out quickly and have reliable outcomes. If we want students to become adaptive experts in the lab, the objective of introductory lab instruction must shift its focus from teaching concepts to creating a space that cultivates students' decision-making abilities while supporting their skill development. This dissertation describes a new introductory physics lab format that supports students' adaptive expertise. The new curriculum was developed for a large-enrollment introductory calculus-based mechanics course at a large Midwestern university. The instructional model prioritizes student agency and decision-making, while developing relevant experimental skills that support expert-like decisions. Simultaneously, the reformed lab leverages the affordances of the Interactive Online Laboratory (IOLab) data acquisition system to encourage ownership and ingenuity. A lab practical exam was used during the pilot stage to determine the effects of the new lab format on students, as compared to students from the concept focused lab. Two studies examined the link between students' skills and the decisions they made. In the first study, video analysis was used to identify student actions as they completed an unstructured lab activity. While all students were able to design measurement techniques, students from the new lab format were more likely to engage in higher-order thinking about their experiment. In the second study, students' responses to data analysis questions revealed they generally used methods they were taught in class and were influenced by expectations about the purpose of physics experiments and by the salience of features in data.