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
DIY Portable LEGO Kit with Free Printable Activity Cards. I like this for school, older kids can have activity cards to create planets/atoms/molecules/fractions, younger ones can practice fine motor skills.