This paper presents a case study of a teaching intervention designed to enrich Year 2 students' theory of biology through the introduction of causal mechanisms of inheritance such as the gene and DNA. The researchers worked collaboratively with the classroom teacher to design the intervention based on the students' prior knowledge of living things and inheritance. Methods used to evaluate the intervention included comprehensive pre-instructional and post-instructional interviews with all students in the class. Classroom observations were constructed as a reflective diary. Findings indicate that meaningful learning occurred as a result of the intervention for many of the students in the class. For these students, networks of knowledge were developed between their understandings of living and non-living things, their understandings of inheritance, and concepts of the gene and DNA. (Contains 3 tables and 2 figures.)