Assessing silent reading fluency in classroom environments is challenging. This article reports on a method of assessing silent reading using underlining, an approach that solves many problems other silent reading fluency assessment measures face. This method computationally monitors readers' silent reading fluency by the speed they underline words in a text. Traditional silent reading fluency measures were compared with the new underlining methodology. Fourth- and sixth-grade students completed silent reading fluency measures (i.e., moving windows, underlining, and paper-and-pencil reading tasks), along with measures of their oral reading fluency, reading comprehension, and vocabulary knowledge. Strong alternate-form reliability coefficients were found for underlining, which significantly correlated with other measures of silent reading fluency and reading comprehension. Underlining methodology also correlated with common language factors, such as word length and word frequency. Together, these results provide support for the psychometric properties of underlining and suggest that it is a promising alternative method of assessing silent reading fluency.