本研究旨在探究小組同儕互評融入國中寫作教學領域，對八年級學生寫作表現及寫作動機的影響。 研究者採用準實驗研究法之不等組前、後測設計，研究對象為新竹縣某國中八年級兩個班級的學生共64人，按班級隨機分派到兩組實驗組，兩組在寫作課時皆進行九週小組同儕互評，其中一組實驗組的小組採能力異質性分組方式進行，另一組則採同質性分組方式來進行。兩組學生於實驗進行前與結束後，均接受「作文評分量表」與「寫作動機量表」的測量。就所得資料以單因子共變數分析等方法進行統計分析，主要研究發現如下: 1.以異質性分組進行同儕互評的學生在寫作能力的整體表現與「立意取材」、「結構組織」、「格式句讀」等三個向度的後測表現皆顯著優於以同質性分組的學生。 2.以異質性分組進行同儕互評的學生在寫作動機的整體表現與寫作動機的各向度表現與同質性分組的學生無差異。 最後，研究者針對本研究的限制進行說明，並依據研究結果提出建議，供未來教學與研究實施的參考。 The study aimed to integrate the strategy of peer-assessment, using different grouping methods, into Mandarin composition lessons and explored its impact on enhancing students’ writing performance and motivation. A nonequivalent pre-and-posttest quasi-experimental design was implemented. Sixty-four 8th grade junior high students from two classes in Hsinchu County were recruited and randomly assigned to two intervention conditions. The subjects assigned to the first intervention condition worked in the heterogeneous groups during the peer-assessment activity; while the subjects in the second intervention worked in the homogeneous groups.The whole experiment lasted for 9 weeks, with a total of 405 minutes. Both of the subjects’ writing performance and motivation toward writing were measured by validated instrument. ANCOVA was performed.The results showed that the subjects working in the heterogeneous groups performed significantly better than those working in the homogeneous groups in their writing, especially in the aspects of selection of materials and topics,organization and rules. However, no significant differences between the two groups in their writing motivation were found .The implications and suggestions for teachers and future research were discussed.