Two experimental techniques, forward recoil spectrometry (FRES) and size exclusion chromatography with fluorescence detection (SEC/fluorescence), have been used to monitor independently the extent of reaction between model end-functional polymers at a PS/PMMA interface. Bilayer samples comprising a polystyrene layer containing ca. 8.4 wt % of amino-terminal deuterated polystyrene (dPS-NH2, M = 22 000 g/mol) on an anhydride-terminal fluorescent poly(methyl methacrylate) (*PMMA-anh, M = 31 200 g/mol) layer were annealed at 174 degreesC for various periods. An interfacial excess observed in the FRES concentration profiles of the dPS-NH2 in the PS layer was used to determine an interfacial coverage of diblock copolymer and a conversion of dPS-NH2 to diblock copolymer. Similarly, the conversion of the fluorescent *PMMA-anh to diblock copolymer was measured using SEC coupled with a fluorescence detector. Both techniques indicate similar reaction kinetics: the formation of copolymer in the interfacial region continued over several hours and approached a steady-state value after 24 h. Interfacial coverages determined from both methods typically agreed to within 15-20%. This validation of the fluorescence approach is important for further investigation of polymer-polymer reaction kinetics and interfacial segregation during in situ reactive polymer compatibilization.