Asynchronous online discussion (AOD) is an essential component of blended learning, and role assignment and timing are two important discussion design considerations. With the purpose of improving blended learning through effective AOD design, this study conducted a two-level factorial experiment to explore the main effects and interaction effects of role assignment and timing on blended learning outcome and experiences. In addition, this experiment examined the influence of role assignment and timing on participants' social communication in AOD and the effects of timing on individual role performance in role-based discussion. A total of 114 participants in a blended course were randomly assigned to four experimental conditions: role-based pre-class discussion (n = 29), role-free pre-class discussion (n = 29), role-based post-class discussion (n = 28), and role-free post-class discussion (n = 28). The results showed that the role assignment strategy featured by initiator, supporter, and arguer has led to improved learning experiences in terms of affection, sense of community, and forum experiences, as well as enhanced social communication in AOD; while timing affected the enactment, contribution, and participation of assigned roles in role-based discussions. However, there was no significant interaction between the two AOD strategies. In general, role-based post-class AOD is recommended after face-to-face lesson because of the better learning experience and role performance.

异步在线讨论（AOD）是混合学习的重要组成部分，角色分配和时间安排是讨论设计的两个重要考虑因素。为了通过有效的AOD设计改进混合式学习，本研究进行了两水平析因实验，探讨角色分配和时间安排对混合式学习成果和体验的主效应和交互作用。此外，本实验还考察了AOD中角色分配和时间安排对参与者社交沟通的影响以及基于角色的讨论中时间安排对个人角色表现的影响。混合课程共有 114 名参与者被随机分配到四种实验条件：基于角色的课前讨论 ( n  = 29)、无角色的课前讨论 (n = 29)、基于角色的课后讨论( n  = 28)，以及无角色的课后讨论 (n = 28)。结果表明，以发起者、支持者和争论者为特征的角色分配策略改善了情感、社区意识和论坛体验方面的学习体验，并增强了 AOD 中的社交沟通；而时间安排会影响指定角色在基于角色的讨论中的制定、贡献和参与。然而，两种 AOD 策略之间没有显着的交互作用。一般来说，基于角色的课后AOD建议在面授课程后进行，因为这样可以获得更好的学习体验和角色表现。