To fully exploit the dispatchable potential of electric-vehicle (EV) clusters, a real-time EV charging and discharging scheduling strategy is proposed that takes into account users' willingness to participate in vehicle-to-grid (V2G) discharging. First, considering the battery degradation incurred during participation in scheduling, an additional economic subsidy is provided, and based on consumer psychology, a response-rate function is introduced to quantify the uncertainty in how users' discharge willingness varies with the subsidy level. Second, using the grid dispatch center's real-time load forecasts together with the online status of EVs, charging and discharging power commands are rapidly re-optimized in each scheduling cycle via a sliding-window mechanism to achieve adaptive real-time control. Finally, case-study simulations verify that the proposed strategy can respond in real time to random EV-cluster access and grid load fluctuations while achieving dual optimization on both the distribution-grid side and the user side.