Saw these style boards on Oriental Trading for use as geometry boards. Wondered a diy hack. Use glue on bottom circle of thumbtack to secure it from being plucked out by little fingers. Sowdering About in Seattle: Toddler Busy Boxes
How to Make a Cardboard Box Marble Labyrinth Game - Frugal Fun For Boys Engineering STEM activity for kids - Build a cardboard box marble labyrinth! Get the marble through the course without it dropping into the holes.