My son has ADHD/Aspergers, and is now in 4th grade. He is able to spend most of the day in the regular classroom, but still gets pulled out to work in smaller groups for writing and speech.
He did OK in pre-k, but it really depends on the teachers. Some of the inexperienced teachers didn't know how to deal with him. One teacher gave him more individual attention. She had him sit on her lap for circle time(otherwise he couldn't sit still). They had more sensory experiences available in pre-k, such as a sand table, ball pit, and body sock. They had him hold a sticky ball of tape, a beanbag, or a stretchy necklace he could chew. There wasn't as much emphasis on sitting still all the time. He was pulled out of the classroom for one on one speech therapy to avoid the distractions.
Then the switch to kindergarten, they had to start over and make a new plan. For most of the year, he had an aide with him all the time to keep him on task. Unfortunately, she was not trained well. She forgot that even though my son might be moving around and look distracted, he was still listening. He'd come home and repeat the aide's gossip with the teacher(like details about someone's surgery). His aide in 1st and 2nd grade had the right training. She understood that his behavior was caused by the ADHD(not bad parenting like the first aide seemed to think), consistently followed the strategies laid out in the IEP, and did not take his outbursts personally. She was amazing and went on to become a teacher. She helped him use a picture schedule to stay on task, take breaks when he was getting overwhelmed or out of control, and could pull him out of the classroom to work with him one on one if needed. They found things for him to do to use some of his extra energy such as helping deliver copy paper or moving books in the library. They tried adding a rocking cushion to his chair. He also had a choice of sitting with the other kids, at a desk at the front near the teacher, or at a separate desk at the back of the classroom away from distractions. They tried to reduce unstructured time(sitting with other kids in the loud, crowded lunchroom), and allowed him to listen to books on tape in the library which calmed him down. They used a reward system to motivate him, and tried to find ways to relate to topics he likes because that would increase his attention span. They also used a "first, then" approach. First you do the teacher's worksheet, then you can do a maze.
We finally started him on ADHD meds during the 2nd half of 2nd grade. He was able to catch up to grade level in math and no longer needs an aide. He starts off the day with the speech teacher as his "homeroom" and they go over his schedule one on one before he joins the larger classroom.