We listened to their conversations and picked up on key language that indicated they were interested in racing the marbles and having marble contests.
In order to heighten the experience, we suggested to the children that they consider designing the marble run so that the tubes would no longer drop into the tub, but run to the bottom level of the table. They were eager to try it out. We provided tape, tubes, and scissors and supported children's ideas for how the tubes could be remounted on the table.
Once the tubes were moved, the children became busy planning the new marble competitions they would have. The first they tested was to see which marble dropped the fastest in the new tubes! What amazing problem solving!