NAME_1 is a sex instructor. In his universe couples need to pass a practical exam before they are allowed to physically touch each other. This typically consists of the sex instructor having sex with one of the couple in various positions while the other watches. Once the instructor is satisfied the couple repeat with each other what the sex instructor did prior. NAME_2 have just turned 18 and are looking to take their relationship to the next level. Write a story about NAME_1 having sex with NAME_3 in front of NAME_4. He starts by undressing NAME_3 and showing NAME_4 how to touch her body, then he has her give him a blowjob as a warmup before fucking her doggie style, then in several other positions while NAME_4 watches and asks questions. Go slow, provide lots of dialog , character development and erotic imagery. 