Considerable effort has been exerted to identify effective instructional methods to teach reading in the early grades. Ideally, these practices would be provided to students by knowledgeable educators. However, many educators lack linguistic knowledge of the English language and essential concepts about early literacy acquisition that predict student reading outcomes. Furthermore, the in-service training needed to fill gaps in educator knowledge is costly and challenging to deliver at scale. Online educator training has the potential to provide a cost-effective, more readily scalable option. However, limited research has explored the efficacy of online training to increase educator knowledge of early grade reading. The current study was conducted to test the effectiveness of online training to improve educators' knowledge of early grade reading concepts. Educators (N = 86 in the analytic sample) who primarily supported students in grades K-5 were assigned randomly to one of three training conditions: waitlist control, in-person, or online. They all completed a test before and after receiving training that assessed their knowledge of early-grade reading concepts. An ANCOVA that controlled for baseline knowledge revealed that educators who received training either in-person or online had increased knowledge of early grade reading after the training relative to the waitlist control group. Furthermore, educators who received in-person training outperformed educators who received online training. This study suggests that online training provides a viable alternative to in-person in-service training and highlights a need to consider ways of enhancing the impact of online training on educator knowledge.