本文探索網路不同小組成員之間跨界(boundary crossing)的活動，跨界環境裡的人際網絡會不會湧現什麼新的學習機會？本研究資料來自於網路討論區紀錄與訪談。三百多位高中生分成56個小組，線上合作長達六週，成員在「小組討論區」發展出自己的運作，使得小組學習同時也是在經營實踐社群(communities of practice, COP)活動；不同小組跨界交談也有一個「跨組討論區」，形成一個壯闊的實踐星群(constellations of practice)景觀。本研究挑戰一般人對合作學習僅發生於組內的預設，揭露各實踐社群成員的跨界行為帶來豐沛的學習，人際網絡提供學習活動有效的支持。其中，跨界成員互動層次不一，分為活躍者、投入者、與周邊者三種類型的仲介者，各有不同興趣能力，展現不同風貌，共同創造出一種集體的仲介實踐(collective brokering practice)。

This study analyzes boundary-crossing participants’ activities in a virtual environment. Research on collaborative learning quite often focuses on interaction within a group and pays little attention to interaction among groups, which has conventionally been considered as irrelevant to learning. Is there any learning occurred when learners cross boundaries? Data were mainly collected from postings and interviews of a six-week inquiry-based scientific activity. 353 voluntary high school students were assigned to 56 groups with 6 members in each group. Two kinds of forums were available. One was designed for discussion of 6 group members only, Within-Group Forums (WGFs). The other was designed for cross-group discussion, the Cross-Group Forum (CGF). One-third of participants went out to CGF and sought new sociation to satisfy their needs. Although they belonged to different COPs, they related to each other at the level of constellations of practice. It was this practice that motivated them to be interconnected with each other. Three levels of boundary spanning behaviors were identified. Brokers did not function merely as buffers or negotiators between people from many COPs. Instead, peripheral and intensive brokers contributed their diverse perspectives and problems generated in different COPs; proactive brokers maintained a collegial and dialogical atmosphere by responding to every posting in a timely fashion. As a group, they provided a participative connection from which they collectively accomplished the enterprise of brokering. The newly phenomenon of collective brokering practice in virtual environment is discussed in detail.