Is it still prostitution if goods instead of money change hands?

Is it still prostitution if less than 25% of the time the sex is in exchange for goods instead of money? If the girls trading the sex are in high school and their clientele are their fellow students, is it prostitution? If it is prostitution, is it because there is money involved or those times money passes straight across? It would not be anything illegal if they were just whores boinking their fellow male students and getting nothing for it. The times where they agree to boink one of their schoolmates in exchange for concert ticket, clothes, software, laptops (they get the expensive goods 1st and give the hapless horndog credit on future romps), etc. is that illegal because not actual money changed hands and often not at the point they are actually boinking?

(To kill off the statutory rape thoughts, they only do high school and Jr. high kids)