This NCEE Technical Methods Paper compares the estimated impacts of an educational intervention using experimental and regression discontinuity (RD) study designs. The analysis used data from two large-scale randomized controlled trials--the Education Technology Evaluation and the Teach for America Study--to provide evidence on the performance of RD estimators in two specific contexts. More generally, the report presents and implements a method for examining the performance of RD estimators that could be used in other contexts. The study found that the RD and experimental designs produced impact estimates that were meaningful in size, though not significantly different from one another. The study also found that manipulation of the assignment variable in RD designs can substantially influence RD impact estimates, particularly if manipulation is related to the outcome and occurs close to the assignment variable's cutoff value. Appended are: (1) RD Low Estimation of the Impact of Ed Tech and TFA; (2) Exploring Heterogeneity in Experimental Impact Estimates; (3) Manipulation of the Assignment Variable; and (4) Simulating Data for the RD Replication Exercise. (Contains 46 tables, 54 figures and 63 footnotes.)