This tudy involves action research by the first author to explore the fectivenes of the Predict-Observe-Explain (POE) technique in diagnosingstudents' understanding of science
and in identifying their levels of achievement. A multidimensional interpretive framework is employed to interpret students' understanding of science. Of prime interest in this paper are students' understanding of science concepts from an ontological and epistemological perspectives. The research methodology incorporates constructivist action-inquiry principles, grounded theory development and triangulation of multiple data sources, multiple data colection methods and multiple theoretical perspectives. Data sources include students' writen POE tasks responses, interviews with individual students, and in-clas discusions with students.