Children had to make a marble run in the group of 3 and the problem was to maximise the time to be taken by the marble to reach at the end. 

It was very interesting to see that children were using different models of marble roller and every group was making their own design. They were trying to maximise the distance travelled by marble, some groups had pasted ice cream sticks and tapes to create more friction in the path of the marble. Two groups had also rubbed the surface of the paper and crumbled it to create more friction. Only one group was not able to use science effectively in their model. click to see image