This resource presents, for the first time, a clear derivation of the equation of a parabola involving its focus, vertex, directrix, and latus rectum. It is designed as both a structured lesson and a printable activity with complete solutions. The material is ideal for use in secondary school mathematics classrooms (Grades 9–12 / ages 14–18) and aligns with key topics in the algebra and coordinate geometry sections of international curricula such as Cambridge IGCSE, O/A Levels, and comparable high school standards. The study duration is approximately 40–60 minutes, making it suitable for a single classroom session or independent practice. Teachers can use it for step-by-step instruction, while students can engage in guided exploration that builds both procedural fluency and conceptual understanding. The resource is equally valuable for educational institutions seeking to provide high-quality, activity-based mathematics content that inspires innovative thinking and problem-solving attitudes in learners.