Thanks to a link from Ann C., I found a copy of an article by Richard Wanderman on assistive technology and learning disabilities,  "Tools and Dyslexia: Issues and Ideas".

Some highlights:

• The label “assistive technology” is redundant: all technology is assistive.
• Discussion of how "tools can be used as levers - to extend what we can do, but they can
  also be used to end-run problems we have with underlying understanding."
• Discussion of the need of practice to become expert with tools.  (Many school districts buy the tools but neglect the practice).
• Discussion of understanding "mistake tolerance".  Wanderman makes the point that "Learning happens when you make a mistake, form a theory on how to
  correct it, test the theory, and move on or go back and try again.
  Mistakes are an essential part of learning."
• Discussion of tool complexity. "Simple is Better if You Want to Focus on Work"
• Examples of side effects of using tools that you might not consider.
• An in-depth discussion of Wanderman's personal toolkit.