Hi Irene can you explain what you mean by special cognitive needs? Perhaps the following helps?
I teach a group of dyslexic maths students - remedial maths. Many struggle with reading and writing. Moodle often allows me to cut down on the amount of extraneous typing they need to do. Here are some comments on the good things-
All paper work and web links are on site - avoids the agony of spelling long links and having to have all notes organised.
We use 'assignment' a lot. Typically there is a write on activity sheet in 'word or 'excel'. They save this locally - do whatever and then upload
a version for feedback. This avoids a lot of writing(which they find difficult), keeps them organised and they enjoy seeing there progress via the log.
The students return again and again to some resources.
I can easily point some students to moodle resources - that I prepared earlier - while focusing on others needs.
We display things that we have made - matching quizzes, images, spreadsheets etc.
The students like chat - but I don't think they talk much about maths!
The language requirements of forums is too daunting.
We had a big failure with wiki's - waiting for version 1.5 before trying again.
Quizzes are good - but my students like working together-and so results have been very qualitative. These are time consuming to prepare.
Hope that helps.