I have seperated my observations of attn to three seperate categories, two being the span or length of the ability to attend to task, and the other being the ability to enter into tasks. Meaning that even if Mary can sit for hours in front of the computer , she still can have great difficulty in school going from math to English to being quiet for general discussion. You might want to check the literature on this point. I have seen kids attend to computer games for lengths of time in excess of the time they attend to other things. By applying software with specific sensory feedback, frequency of feedback, eliminating the pencil writing process, far-point copying, etc, ADHD kids can become much more task persistent and productive at their school work.
Auditory feedback is particularly helpful for some students.
Of course, the sofware has to be relevant and useable to DO actual school work. We can disuss specific programs if this is the kind information you are looking for. I would be most interested in hearing more about the type of software that is available and how it is being used. However I'm keen to hear as much as possible. The client I saw was using a computer for basic maths skills and somme basic games.