In rural, geographically dispersed school districts, access to high-quality face-to-face professional development (PD) is challenging. Our study developed and compared the effectiveness of an online PD for middle-school science teachers working in remote, rural areas of Kansas with an evidence-based traditional face-to-face PD with the goal of supporting change in teachers' conceptual understanding and self-efficacy in utilizing Next Generation Science Standards (NGSS), change in instructional practices, and overall student content learning. Fifteen rural middle-school science teacher participants were randomly selected to participate in the online or traditional PD, then taught the Toward High School Biology curriculum to their 504 middle-school students. Findings aligned with our hypothesis that online PD is as effective as traditional in improving student content knowledge related to the curriculum. Teachers' instructional practices in using Next Generation Science Standards improved, as did their use of student-centered instruction and making science relevant to the lives of their students. Our study supports the importance of designing PD that effectively and economically brings teachers in isolated and diverse rural communities together.