When I think what I wore on my CBT... jeans, combat boots, a pair of ex army NI combat gloves and a yellow traffic coat (OK, it was February) but I learnt and had invested in an HG Voyager jacket and some pathan gloves by the time I did the DAS bit. Still got away with some heavyweight jeans, longjohns and waterproof overtrousers, wouldn't dream of wearing them now tho.
The only people I saw on the CBT with full racing leathers and knee sliders were the women who had previously been out on their husbands/boyfriends bikes as pillions. Not sure what the instructors thought of knee sliders on day one of CBT