we built the bridge going from one side to the other of the bin it would be a good length and the stiff sides would help hold the bridge in position.
this time i allowed students to make support columns for their bridges. some built the legs and some did not. above in the bottom photo, the team added their little columns when the bridge started to sag a little. fabulous improvement!
tip: toothpicks can be very sharp! caution students about this as they begin to work. i do use round toothpicks because they are more sturdy than flat ones.
the first class tried the plastic bins and just built their bridges. i 