Toilet Learning

We have just under 20 Sharks swimming in the tank.  About half of them are in diapers/pull ups during the day (either full time or just for nap).  I can't stand it!  This is my personal least favorite part of the job.  Don't get me wrong, I understand the significance and importance of toilet learning, but as a preschool teacher I have fun elsewhere in the class.  One of my friends is 3.3 (years.months) and is a twin.  She went through diapers/pull ups/underwear and was trained several times.  Over the past few weeks, for the safety of the rest of the class, she's back in pull ups full time.  Now we can barely get her to even pee on the toilet.  She is very bright and knows what she's doing.  She started out just pooping in her pants and saying, "It was an accident.  Accidents happen," and then smiling really big... Now she won't tell us that she's done anything, doesn't let anyone know she needs to go, and we've been having to put creme on her since she's getting red now.  As a teacher, and I know her parents feel the same way, it's very VERY frustrating to have a child regress in toilet learning.  They've talked to their pediatrician and I've been working closely with the office to figure out different strategies and techniques to try, but we've exhausted them.  We were given the green light to start from scratch.  Back to square one.  Starting line.  Seed in the dirt... 

I'm not a toddler teacher.  It is the last place before school aged kids that you would find me working.  With all these preschoolers in diapers it's beginning to feel like I'm leading a toddler class.  I give major props to those hard working, dedicated educators that can handle the needs of tots.  You are amazing!  

Here's what I've been doing with my back-to-basics friend: 

• Put in pull up right at drop off (She wants to wear underwear to school.)
• Once to twice an hour send her to the bathroom
• If she pees/poops in her pull up, she gets undressed and wipes herself before getting wiped by a teacher, then redresses herself
• Given lots of praise when she does anything in the toilet, tells a teacher she needs or has already gone to the bathroom
• Lots of talking about why we should be going potty on the toilet and not in the pull up

Any more/different ideas, suggestions, tricks of the toilet learning trade to share?  Anything and everything is much appreciated!