She uses you for an endurance test

"Your attention everyone," Miss Silverton shouts.

"Today, we are going to test how long each of you can hold your breath underwater. John here, will be standing in water up to his chest."

"When I say 'Start' the girl in front will go underwater and place John's cock in her mouth. You John will hold out your hands and place them under the girl's breasts for support."

"As a bonus, any girl who has cum in her mouth will be free to leave class early."

"Now, get into position."

You slowly get into the water. You notice that the first girl is a redhead with small breasts. The next one is a blonde with average tits. Further on is a black-haired girl with large nipples.

The redhead dives into the water and takes your semi-limp cock into her mouth. You move your hands under her breasts.