Keep early finishers on task with 20 mini STEM design challenges that use simple materials (index cards, tape, cups, straws). Each card includes a clear goal, material limits, time box, and a simple test, plus a one-line student reflection. Includes Teacher Guide, Safety & Norms, Materials Menu, Score Sheet, 4-Point Rubric, and Certificate. Ideal for STEM centers, sub days, and STEM Friday in grades 3–6. Sample challenges: Index-Card Tower, Paper Bridge, Marker Holder, Marble Maze,