Whilst I was doing my DAS, the school lent me a Yamaha 125 thingy to ride to and from the school each day, about 30 miles. However, I was shocked how car drivers treated me whilst riding the 125. They would constantly try to bully me into the side of the road and attempt to overtake. Yet whilst riding my own Suzi 550 (bought before passing my test and used during the DAS) with the same riding style and speed they left me alone. On more than one occasion a boot went out in the direction of a car wing
Seems the physical size of the bike did make a difference.
I found the DAS course invaluable, not only to pass the test but also learning to command the road space around you whilst riding. Good for when when mums on the school run pull out on you and you need an exit.