The naive conceptions that children develop tacitly or explicitly, outside the classroom, contribute to their interpretation of the teacher's words, paragraphs in a book, or the results of an experiment. These conceptions (or "alternative frameworks") may persist even in the face of systematic teaching of competing scientific concepts and models. In addition, they can be very resistent to change. The study, an attempt to explore concept formation and attainment by children (N=22) over a period of time, focuses on alternative frameworks and an approach used to examine them. The interview-about-instances (IAI) approach consists of a dyadic interview where the focus of attention is a deck of stimulus cards depicting physics situations which students are required to classify as examples or non-examples of a concept. The approach attempts to describe the conceptual framework students are using rather than present a critical expose of the inadequacies of their thinking. Results of interviews related to the concepts of force and energy indicate that students tended to reply in a general non-specialist way, recognizing situations as "physics" questions, but fluctuating between intuition and algorithm as they answered. It is suggested that effective teaching involves building on the students' pre-determined knowledge. (JN)