The purpose of this study was to determine whether a walking program supplemented by tasks designed to challenge balance and mobility (WALK+) could improve physical function more than a traditional walking program (WALK) in older adults at risk for mobility disability. 31 community-dwelling older adults (M +/- SD age = 76 +/- 5 yr; Short Physical Performance Battery SPPB score = 8.4 +/- 1.7) were randomized to treatment. Both interventions were 18 sessions (1 hr, 3x/wk) and progressive in intensity and duration. Physical function was assessed using the SPPB and the 400-m-walk time. A subset of participants in the WALK group who had relatively lower baseline function showed only small improvement in their SPPB scores after the intervention (0.3 +/- 0.5), whereas a subset of participants in the WALK+ group with low baseline function showed substantial improvement in their SPPB scores (2.2 +/- 0.7). These preliminary data underscore the potential importance of tailoring interventions for older adults based on baseline levels of physical function.