Explore gravitational lensing with a free high-school physics lesson, printable worksheets, teacher answers and standards-aligned activities. For grades 9–12 / ages 14–18, with introductory college extensions. Investigate multiple images, relative arrival times, geometry, gravitational-potential timing and mirrored image parity. Includes a seven-page teaching packet, guided tasks, worked answers, assessment rubric, standards mapping, semantic HTML lesson, plain-text response template and a teacher ZIP with model cases and an optional offline Python checker. Allow 45–55 minutes, or 35–40 without the algebra extension. A calculator is sufficient for the paper route. Prerequisites: signed arithmetic, subtraction, division and unit conversion; Task 4 adds formula rearrangement. Publisher-authored mappings cover selected NGSS Practices 2, 5 and 6 and Crosscutting Concept 4, plus CCSS HSN.Q.A.1 and HSA.CED.A.4 (Task 4 required). This does not claim completion of an entire NGSS performance expectation. No student account, payment or online answer submission is required. Downloaded paper/HTML materials work offline. The optional verifier requires Python 3.9+ and its standard library. The PDF includes tagged reading order, headings/bookmarks, table headers, descriptive links and diagram alternative text. Generated teaching-model cases are distinguished from real astronomical observations. This TES edition licenses the original teaching materials and original code included in its kit under Creative Commons Attribution 4.0 (CC BY 4.0), permitting sharing and adaptation, including commercial use, with attribution. Logos/branding, separately credited third-party materials and other website content retain their own terms. Explore the interactive lesson on our website: Gravitational Lensing Lab — Dark Science Docs.