Ok, here I am dressed exactly as you described, Schoolgirl, plaid skirt, black tights and yes, I am wearing panties.
Now for your part of the deal!!!
Pull your trousers down, let me see, you have to be wearing those white see-thru panties and those natural coloured pair of tights I gave you.
Wow, look at you, my god look at the buldge in those panties, its almost obscene!!
When was the last time you had a wank?
A week, good, lets see if we can make the tip of your cock drip and make the crotch of your panties wet with pre-cum