What exactly do you want to know?
My son was diagnosed with ADHD last year, in the spring of his 2nd grade year. His primary teacher had sort of hinted around at it, but his lower elementary teacher (who is wonderful) wanted to wait because she said most 1st/early second graders take a while to "settle down." At his Spring p/t conference last year she mentioned the fact that she suspected his issues were "organic" and we had already come to the conclusion that we wanted him tested. We had her fill out the Connor's forms and he was diagnosed. We tried some medications and kept in touch with his teacher via email about his progress. Stimulants didn't work well for him (he developed emotional issues and tics), so he has been on Intuniv since the end of school last year. He definitely still has attention issues, but his teacher is trying to work on helping him learn to manage those by initiating measures like him asking to go work in the hall/library/office if he is having trouble focusing. The hard part is getting HIM to recognize it without being reminded.
He is doing well in the Montessori environment and I have nothing but good things to say about how his teacher and the school have handled things. The good things about Montessori and ADHD are the kids can get up and move around, they can choose work and projects that truly interest them. His teacher is also the mom of a grown ADHD daughter, so she has been especially understanding! Now we are facing the choice of going on to upper elementary or moving to a public school environment. Money provided we will probably stay with Montessori for upper elementary, although we are concerned about whether it is the best choice for him academically or not and worried about how a different teacher will deal with things. His primary teacher didn't handle him well at all. The upper el teacher has a daughter with ADD -- inattentive, so maybe/hopefully she would be understanding about the challenges.
Does that help? Is there anything more specific you were wondering about?
Ds isn't diagnosed with ADHD yet, but it's coming down the pipe, I'm sure. I think I will choose to not put him on medication (at least not until he is older). If I seek the dx, it will be to get him accommodations in the schools (he's in a public M). Frankly, the accommodations I would ask for should be built into a good M program...but he's not in a "good" M program. ;-) (I don't like the new emoticon process, so I have reverted to my old standby.)
What are your specific concerns for your ds? Some people see good results with meds (Montessori or not), but a lot of times there are steps to try beforehand.
When my ds was 6, he definitely presented with behaviors many would think were ADHD like. His was most definitely sensory integration and with the addition of a good sensory diet he was able to be successful, not have the behaviors as much and very importantly we had the most spectacular lower el teacher to help. With time, help from an OT and his phenomenal teacher by the end of 2nd my ds was able to recognize his sensory needs on his own and take care of them most of the time. Third grade was everything a third grade year should be in terms of his development, being a leader and helper with the younger students, and enjoying the process of learning.
By the way, my ds was a crasher and banger type kid. When he would feel out of balance, sensory deprived he would move about in inappropriate ways, act up, be disruptive....adding in activities that used his big muscles (practical life type things such as sweeping, vacuuming the front office at school, taking out trash, chewing gum, having asnack that was really crunchy etc) his need to behave inappropriately diminished and vanished. He learned with time to take care of his needs. To this day he might be sitting and working on something and then get up, go outside and run around our house several times...come back inside and return to work with focus and discipline. Getting older and having the tools to be successful have done wonderful things. He is amazing.
A long way of saying it is worthwhile to investigate whether it is adhd, sensory integration, some combination or something. If nothing else, you will learn and become aware of things that your ds can use to be successful.