Precise detection and localization of learners' engagement levels are useful for monitoring their learning quality. In the emotiW Challenge's engagement detection task, we proposed a series of novel improvements, including (a) a cluster-based framework for fast engagement level predictions, (b) a neural network using the attention pooling mechanism, (c) heuristic rules using body posture information, and (d) model ensemble for more accurate and robust predictions. Our experimental results suggest that our proposed methods effectively improved engagement detection performance. On the validation set, our system can reduce the baseline Mean Squared Error (MSE) by about 56%. On the final test set, our system yielded a competitively low MSE of 0.081.