This paper investigates the impact of assignment to the Accelerating Literacy for Adolescents (ALFA) Lab, an additional semester-long class taken during an elective period, on ninth grade student reading achievement, motivation, and frequency. We conducted a regression discontinuity (RD) study where 1,378 students from diverse high schools in four states over three years were assigned either to the treatment (ALFA, n=540) if their score on a pre-assignment reading measure fell below a threshold cutoff or to business as usual (BAU, n=838) if they scored at or above the cutoff. The study found positive but non-significant effects on reading achievement, motivation, and frequency. Bayesian sensitivity analyses suggest positive effects are more likely than not. We discuss several issues that may have contributed to the failure to detect significant impacts: Student absences, student attrition, and limited instructional time due to the COVID-19 pandemic. [This is the in press version of an article published in "Journal of Research on Educational Effectiveness."]