It's a curious and wondrous fact that the sum of the first n cubes is the square of the nth triangular number.
For instance, with n=3, the first three cubes
 here made in Cuisenaire rods  can be reassembled into a square:
The square is six units wide, six being the third triangle number.
The puzzle then, was to make the cubes and then make a square from them. The class managed that successfully and it might have finished there, but when the following day they were asked to create a growing pattern of their own in Cuisenaire rods
four of the girls chose to return to the square of cubes and make it bigger:
and bigger  swallowing up all the Cuisenaire rods in the school, until they had created a monster:
The next day, while the rest of the class explained their own patterns, the four girls enthused about their creation.
It was time to have a closer look at the patterns of numbers hidden inside this huge square:

triangle numbers 
with the invitation to make the cubes and the squares from the same rods:
We rounded it all off by inviting the Year 2s and Year 3s to find out what it was all about. The four girls explained their creation brilliantly!