本研究之目的乃在規劃自然與生活科技學習領域中的「設計並進行實驗之過程技能」的實作評量，並且實踐與探究其效益。研究者以能力指標為本，將之轉化為教學評量目標之後，以此來設計實作任務。經過第一個班級（26名學生）的操作以及修正之後，為有效考慮評量的教學功能，研究者最後確立二階段四要素的實作評量之實施，於第二個班級（25名學生）再次進行。實作評量第一階段的主要工作是讓學生依據評量任務設計實驗，教師批改之後與學生共同討論並修正錯誤的設計；第二階段的主要工作是讓學生以修正後的實驗設計進行實驗操作的過程技能評量。四要素則包含實作任務(performance task)、反應型式(response format)、評分規準(scoring rubrics)、以及後設規準(meta rubrics)。透過積差相關係數、Cronbach's α係數及Kappa一致性係數分析以及學生的表現，研究者認為二階段四要素實作評量可協助教師分析學生的表現結果，並由學生的表現回饋到能力指標，再從能力指標回饋教學，增進實作評量對於教學的助益。

The purpose of this research was to design and conduct a performance assessment on students' ability on implementing experiments. Its effects were also discussed. Related ability indicators were transformed into assessment objectives. There were four essential elements in the assessment objectives: performance task, response format, scoring rubrics, and meta rubrics, to ensure the quality of assessment design. After the pilot test with 26 students and formal test with 25 students, a two-stage assessing procedure was applied to motivate students' learning and understanding. Pearson's r, Cronbach's α, and Kappa's κ all indicated the consistent rating results from two raters. This study concluded that the two-stage four-element performance assessment functioned as a mediator to depict students' ability structure, enhance their designing ability and provide teachers with feedback on teaching.