Which instructional tool is recognized as the most common, flexible, and economical?

The overhead projector is considered the most common, flexible, and economical instructional tool because it allows instructors to present visual material in a way that engages students effectively. Instructors can project transparencies that can illustrate complex concepts, showcase diagrams, or highlight key points during lessons. This adaptability makes it suitable for a wide range of subjects and teaching styles.

Moreover, the overhead projector is economical as it typically requires minimal investment compared to other high-tech presentation tools. It can be used repeatedly with different transparencies and doesn't incur ongoing costs like digital presentation software or hardware might. This makes it an appealing choice for educators working within budget constraints.

Additionally, the overhead projector's flexibility allows instructors to modify their presentations on the fly, writing or drawing directly onto the transparencies in real-time, which can enhance interactivity and student engagement in the classroom context. This adaptability and cost-effective nature solidify its status as a favored instructional tool among educators.