Powdered Borax can irritate the skin if left in contact with it. Children under 12 years of age should be supervised by a responsible adult. Add food coloring, if desired. Knead well for several minutes. At first, it will be very sticky, then less so as you knead it.
Some experimenters like to add a small amount of liquid laundry starch to the mix.
Sometimes this makes the material slimier, and sometimes it doesn't mix in very well. Try to pick up newsprint from a paper with this stuff. Elmer's School Glue is mostly Polyvinyl acetate. The molecule is long and thin, like the Polyvinyl alcohol used in last month's experiment. Again, the borax is the cross-linking agent, but the mechanism is not as well understood.