Hi
It can work in whatever way you want it to really. Personally I have a consultant and do all the tutoring myself - I spend very little time sitting across a table with DS focussing on targets but do incorporate the principles of ABA into everyday life which means I interact with DS in a very different way to the way that I did previously. I also try to ensure that the other people who spend a lot of time with DS do what I do or at the very least don't undo what I do.
I am being trained by my consultant and also read a couple of manuals eg Motivation towards Recovery which were really helpful.
The biggest improvements have been in speech, eye contact, seeking the company of others instead of playing alone. He used to have obsessions that changed every month or so - now that I don't allow him to have so much unstructured time and try to keep him engaged he doesn't seem to have obsessions in the same way. At one time his obsessions were all consuming and you couldn't break through them. He answers us now when we ask him questions most of the time.
I think ABA is great but I do think there are a lot of sharks around who will persuade you that you have to spend 35-40 hours a week to see progress and you have to engage tutors. I just don't think this is true. Of course if both parents work 10 hours a day 5 days a week then tutors will be necessary. In my case I work 3 days a week so have some free time. I don't stick rigidly to trials. I have in mind the targets/goals and try to achieve them by incorporating them into everyday life eg if we are categorising then I will take him to the supermarket and ask him to choose his fruit or vegetables for the week.
The main thing about ABA is keeping your child engaged and making him/her feel that it is more worthwhile to be with other people than it is to be alone and that life is easier when you ask for things instead of tantrumming/shouting/crying and having people guess what's wrong.
Dolfrog wants facts and stats. I don't have them - all I can say is that the general principles of ABA have fitted into our budget, our lifestyle and our parenting ethos very well. Maybe strictly speaking what we are doing is VBA - so what, who cares. Whatever it is, it's working and it's wonderful to see a disconnected child become connected with the world, to say of his own accord "I'm happy" and "I love you".
Good luck with whatever you decide to do. Please don't be scared off by the 40 hours a week stuff - a provider told me that to begin with - if you need consultant recommendations there are plenty of us that can help if you want to PM us.