St. Patrick's Day Leprechaun Trap STEM Project-Based Learning is here! This STEM activity and challenge for 2nd-3rd graders uses the concepts of simple machines (pulleys, levers, inclined planes/ramps) and the engineering design process to engage students in the challenge of building a leprechaun trap that can trap and contain a marble or ping pong ball (representing a leprechaun). Step-by-step directions and materials list are both provided for the teacher to allow for maximum student success.