Children who have poor fine motor skills and difficulty with handwriting or handwriting speed may find that using a keyboard will assist them in the classroom.

"Sticky keys" may aid in typing with one hand. Microsoft Operating systems (and possibly other operating systems) have located in Control Panel/Accessibility Options this aid which allows the keyboarder to hit the access keys like "shift", "control", "alt" once to activate them and then release and hit the accented key. .

There are several options for people who can't type with two hands.  The one that is getting the most press right now is voice-recognition, but this is still pretty crude -- most packages require a lot of 'training' -- you say each word you want the computer to recognize 10 times each! It can take hours and hours. There are also adapted keyboards -- smaller ones, ones with different arrangements so that all the most commonly used keys are in the middle, etc... There are also software solutions -- e.g. one called 1/2 QWERTY that maps the one half of the keyboard on to the other half. eg. you get a g if you hold down the spacebar and hit h.

Some OTs suggest that the children practice 1-handed typing on the regular keyboard (if that's what every one else is using) to start. Early typing lessons tend to be a lot of just getting to know where all the keys are. There are teaching materials available for this, including a manual called "Type with One Hand" that dates back to the 50s. There's also a computer tutorial called "5 Finger Typist". 

Have your school OT set up a system that will work best for your child's class situation. You could try to have the child follow the regular typing curriculum as much as they can, using adapted hand placement. As they get older and are cognitively ready to start writing stories, editing, etc., it is easier to tell what alternate keyboard or software (if any) would be useful. And they are still learning to use the regular keyboard which is an excellent life-skill! (eg. in the library, at an internet cafe, if they just want to look something up quickly at school, or if they don't have the dexterity to plug-in their adapted keyboard by themselves, and the regular one is left on, etc).