Guiding students to generate testable scientific questions is essential in the inquiry classroom, but it is not easy. The purpose of the BDC ("Big Idea, Divergent Thinking, and Convergent Thinking") instructional model is to to scaffold students' inquiry learning. We illustrate the use of this model with an example lesson, designed to help 5th-grade students understand the concept of plant growth. The BDC model functions as an exploration of, and a connection with, related information among students' scientific knowledge, skills, and practice, so that students can further generate research ideas. Students are able to more easily formulate testable questions and are also highly motivated throughout the course of their inquiry practice. This instructional model provides teachers with a practical and meaningful tool, one that increases students' capabilities to formulate researchable questions and sustains their motivation to engage in activities of scientific and creative inquiry.