Lots of you sent us excellent solutions for The Third Dimension. Chris and Michael from Moorfield Junior School, and Lily and Ruth from Brecknock Primary School in Camden managed to find eight arrangements altogether, including the one which we drew in the question. Lily explains how she systematically looked for them all:

To do this problem I used unifix cubes to help me. First I started with a long block, then I took one cube off and moved it to different positions making sure I didn't do the same one twice. I kept the cube in the middle and moved a second cube from the end to make a square. After that I moved this brick into further positions.

Here is Ruth's drawing which shows these arrangements very clearly:

eight arrangements of four cubes joined together