In order to encourage students to participate in online learning forums, prompt responses to their questions are essential. To answer students' online questions, teaching assistants are assigned to manage discussions and answer questions in online learning forums. To minimize the response time, many teaching assistants may be needed to interact with learners. We investigated the trade-off between the request-response time and the cost of labor for handling the requests since this has become a challenging and important issue for education managers. In this study, a queuing-based model is proposed to construct the relationship between response time and the human resource requirement in a learning forum. In addition, an experiment using students in a Computer Science Introduction course at a vocational high school was conducted to verify the model and determine the average number of assistants required so that the students' questions can be answered within an acceptable time interval, providing valuable information for managing online discussion forums for educational purposes. Finally, the participants' perceptions were investigated using a questionnaire revised from the Technology Acceptance Model (TAM) in order to identify whether feelings of the perception-of-usefulness and the perception-of-satisfaction during the response wait time showed significant differences when the number of teaching assistants was reduced. The results revealed no significant difference in learners' perceptions after reducing the number of teaching assistants. It confirms that using the model to predict the number of required teaching assistants is highly reliable, and effective in reducing labor costs without jeopardizing student satisfaction.