The current study employed a stimulus equivalence paradigm to assess the ability of the recently developed Function Acquisition Speed Test (FAST) to measure the existence and strength of experimentally produced derived relations. Twenty- two participants were exposed to a One- to- Many stimulus equivalence training procedure (A1–B1, A1–C1, A2–B2, A2–C2), followed by testing for derived B1–C1 and B2–C2 relations. All participants were then exposed to a FAST procedure in which a simple common operant response was established for pairs of equivalent stimuli (e.g., B1 and C1) in one block of training. In another bock of training, a common response was established for pairs of nonequivalent stimuli (e.g., B1 and C2). Trial numbers required for participants to reach mastery criteria differed across the two FAST blocks, as expected, but only for those participants who had passed the prior equivalence testing phase. This finding suggest that the FAST procedure functions as both a concurrent measure of stimulus equivalence class emergence and a functional- analytic tool that might assess unreinforced and socially sensitive stimulus relations formed in the world outside the laboratory. Large inter- and intra- participant variations in performances across FAST blocks are discussed.