It came from of one of my student (15) disappointed by the Random block in Blockly.
It might be worth posting or checking the Blocky code because it could be the way she is using Blockly which is causing the problem.
As with PICAXE Basic, RANDOM affects the variable specified, uses it both as a seed and the next value. If that variable is altered elsewhere in the code it will limit the range of values stepped through, can degrade the randomness significantly.
The attached seemed to give a fairly random result when tested under simulation -
"LLLRLRRLLLRRRRLLRLLLLRLRRRRRLLRLRRRRRRLLLLLL"
For left-right decision making and the like it's usually not the randomness which is a problem, but the feel that it is not random. Randomness doesn't always feel natural and the challenge can be in forcing something to feel more natural than being more random.