L.
Dear M.,
The problem may lie in the preschool. It may have been a great place for him when he was two years old, but the three-year-old class may not be as appropriate. Have you visited the classroom and/or explored other preschool options? Children mature at different rates and learn in different ways. If the teacher (who is supposed to be the expert) is at wit's end, is that your son's problem, or the teacher's problem?
I had similar problems with my only son who is now 9 years old (I have 3 daughters) when he went to a Montessori preschool at age 3. Unknown to me, he was having ear problems due to infections and allergies and couldn't hear well. The teachers complained that he would not follow instructions or commands especially if he wasn't looking at them. I called him the time-out king because he was punished so often. The end result was that I got him speech and hearing help, lots of medicine, and eventually ear tubes, but the teachers had already labeled him a bad boy, so I was forced to switch preschools. It was the best decision that I ever made, because he responded to the new school very well and has never had a behavior problem in school since then.
Also, be sure that his food choices don't involve dyes, sugar, or caffeine, and that this isn't an issue of acting out to attract a classmate's admiration or an adult's attention. Some preschools ignore the well-behaved children.
Hang in there. I'm a single parent too, and it's tough but rewarding.
L.