In-person tutoring programs can have large impacts on K-12 student achievement, but high program costs and limited local supply of tutors have hampered scale-up. Online tutoring provided by volunteers can potentially reach more students in need. We implemented a randomized pilot program of online tutoring that paired college volunteers with middle school students. We estimate consistently positive but statistically insignificant effects on student achievement, 0.07s for math and 0.04s for reading. While our estimated effects are smaller than those for many higher-dosage in-person programs, they are from a significantly lower-cost program delivered within the challenging context of the COVID-19 pandemic.