Many students, even after formal science instruction, have not developed a scientifically acceptable concept of "living,""animal," or "plant." Therefore, as part of the action-research phase of the Learning in Science Project, a working group was formed to explore (with teachers) some possible strategies aimed at modifying students' current concepts toward scientifically acceptable ones. The goal was not to create specific strategies to teach a scientifically acceptable concept, but to set up a learning environment which forces students to challenge their own concepts, and eventually finding them to be inadequate, to see the need to modify them. A survey of student concepts was conducted before and after teachers used materials developed (including detective puzzles and classification/categorization activities). Results indicate increases in the number of students using the scientific meanings of the concepts after the teaching unit. Four implications for science instruction are discussed, including the suggestion that focusing on characteristics of living things, plants, and animals be left until advanced secondary levels. (Included in appendices are highlights of major findings from exploratory/in-depth phases, details of the action-research phase, sample pages from the teaching activities booklet, and graphical representation of pre-/post-survey results.) (JN)