You probably already know what Joy To Key is from my previous entries (a free program that allows you to assign mouse or keyboard actions to any gaming joystick or controller). Click-N-Type is a free, customizable on screen keyboard with word prediction capabilities. It can be used with any pointing device, mouse emulator or touchscreen and it can run in scan mode. It also has text to speech capabilities. There is a built in autoclick/dwell feature. There are over a dozen versions of the keyboard to download and try. (E-mail me or comment if you want to try my own personal "speed keyboard" adapted to require minimum joystick movement, especially for buttons like space, shift and delete.)
A little creative thought and Click-N-Type can be used with learners with cognitive challenges. You could make a board using the Click-N-Type designer that just has the letters of a students name or you could make a board with just numbers for a student to enter answers to math questions or use an onscreen, but not accessible, calculator. You could even make a board of all macros for higher functioning students to use to enter certain strings of text while they are using a regular keyboard. I am sure there are dozens of other ideas as well.
Click-N-Type is a remarkable piece of software and is well worth spending some time getting to know. It is hard to believe it is free, especially when you compare it to other, similar programs (which can cost from to $350 dollars to $500 dollars).