With a big finish.

I spent the rest of the class slowly being teased by each of the girls, any time my penis lost some volume the next student would come up and tug it back to life. As the class wore on, the five seconds each girl was allowed seem to run longer and longer. We managed to go through the entire class but the girls were still volunteering. I didn't want to waste the momentum so I allowed everyone to take a second turn.

I looked over at the clock and there was about 5 mins left in the hour: I wasn't sure how much longer I could take this.

The next girl was Merta back for her second (or was it third?) turn. Before she came up, Bridget stopped her and whispered something in her ear. Both girls giggled and made eye contact with Scarlet and Ingrid. Clearly, something was being planned.

Merta answered her question in a heartbeat (I was struggling to come up with questions that were equally as hard as the first few).

She came over and with both hands this time started stroking me off. There was no pretence anymore, she was openly masturbating me as the class watched. I was about to stop her when suddenly my arms were pulled back behind me. Scarlet and Bridget were standing behind me with, each holding one of my arms. I hadn't even seem them move up to me.

I was about to resist but something in Bridget's eyes told me to go with the flow and just see how things progressed.

I was staring into Bridget's eyes, whilst Merta continued her two handed attack on my penis, picking up speed with each stroke. I felt something cold and wet near my anus and realised Scarlet was trying again to enter. I don't know why but i squeeze down on my hole, given her easier access and Scarlet worked her finger in and out.

"Look out, he's about to explo-"

Before Merta could even finish the sentence I shot out a stream of cum blasting almost three or four feet in front of me, some of it landing on one of girls in crowd. But before anyone could react, another blast. and another. and another.

All up I shot a total of seven or eight times.

"Aaaaand cut. That's a perfect ending." I looked up and of course, there was Ingrid with Scarlet's fancy camera. "This footage will be great for your documentary Scar."

At that moment, the high of the last hour quickly wore and I realised what I'd just done. I'd been masturbated in front of an audience of my students and my girlfriend's mother. I realised that I'd coated some of them in my semen. "oh my gosh girls, i'm so sorry. that was incredibly unprofessional of me." at this point I had covered up my quickly deflating penis with my hands, whilst I offered the towel to the students who shared it in cleaning up.

"it's fine professor. Honestly, what a memorable class."

"Yeah, no complaints here."

At that point, the clock chimed signalling the end of the session. As the girls packed up their bags I stood near the door, clasping my privates whilst the girls left. Some took one last chance to grab my arm, or butt before they walked out.

Soon, it was just Bridget, Scarlet, Ingrid, and Dr Bernard left. I was of course still naked, someone must have taken the towel after the girls cleaned up.

Dr Bernard came up to me. "I must say I am quite impressed, I wouldn't have expected you to agree to all those demands but you really seem up for anything if it means helping your students learn. Plus, you were just as hard on Bridget as you were with everyone else so...I will allow you to continue dating my daughter. But first...you look like you need another shower."

She was right, I looked down and my body was covered in a thin layer of sweat and I smelled strongly of cum..