Cardboard Tube Marble Run

You will need

• Paper towel and toilet paper cardboard tubesCollect 6–10 tubes for a good-length run
• Large piece of cardboardFrom a clean food or household-goods box, as a backing board

  Use only boxes that held food or household goods, not chemicals; wipe the interior clean before use.

• Masking tape or painter's tapeAt least one full roll; this is the primary structural adhesive
• Washable tempera paintTwo or three colors; watercolor also works
• PaintbrushesOne wide, one narrow
• Newspaper or a trash bagTo protect the table surface during painting
• ScissorsAdult pre-cuts the lengthwise slits; child uses rounded-tip scissors for smaller trimming

  Keep adult scissors for the lengthwise tube-cutting step; hand child rounded-tip scissors for all other trimming.

• Marbles or small rubber ballsThree to five; ping-pong balls also work if marbles are unavailable

  Marbles are a choking hazard for any child under 3 in the household; put them away immediately after the activity if younger siblings are present.

• White school glueoptionalOptional reinforcement at tube joints

Steps

1. 1

   Paint the tubes first

   Set out the tubes before assembling anything and invite your child to paint them in whatever colors and patterns they choose. This step dries while you talk through the design, so it does not slow the build phase. Two to three colors of washable tempera is plenty; stripes and dots hold up well on curved surfaces.

   Tip: Roll the tube slowly on the table to reach all sides without waiting for one side to dry.

2. 2

   Plan the run together

   While the tubes dry, lean the cardboard backing against the wall at a shallow angle. Roughly sketch with a finger — not a marker — where each tube might go: one at the top, angling down, connecting to the next. Explain that the marble needs a downhill path the whole way. Ask your child: 'Where do you want the marble to come out at the bottom?'

   Tip: A shallower overall angle makes the marble slow down enough to stay in the tubes rather than jumping out.

3. 3

   Tape the first tube in place

   Start at the top. Hold the first tube against the cardboard at a downward angle and let your child run strips of masking tape across it to hold it. It takes more tape than children expect — show them to press each strip firmly on both the tube and the cardboard. Two to three strips per tube is the minimum.

   Tip: An X of tape over the tube holds better than parallel strips.

4. 4

   Add tubes one at a time

   Work downward, adding one tube at a time and doing a test roll before taping the next. Hold the following tube in position and drop a marble in to see if it flows across the gap. Adjust the height and angle of the receiving tube until the marble rolls in cleanly, then tape it down.

   Tip: Gaps between tubes work fine as long as the receiving tube is positioned slightly lower and directly in the marble's path.

5. 5

   Troubleshoot stuck spots

   When the marble stops mid-run, which it will, help your child identify where it stopped and why. Usually a tube is not angled steeply enough, or a gap is too wide. Say: 'The marble stopped here — what would happen if we tilted this tube a little more?' Let your child make the adjustment before you suggest the fix.

   Tip: Bending one of the pre-slit tubes into a curve is often the fix for an awkward gap.

6. 6

   Add a catcher at the bottom

   Tape an open box, a bowl, or a cup at the base of the run to catch the marble at the end. This completes the run visually and practically — the marble landing in the catcher is the satisfying payoff. Let your child name the machine and, if they want, label the catcher with washable marker.

   Tip: A small cardboard box makes a loud, satisfying sound when the marble lands in it.

Take it to the table

Materials checklist, the steps and the variations on one Letter page.