I work with children with special needs and have found Ziptales to be very helpful for younger children and Literacy Planet (depending on their level of Literacy).
Ziptales provide audible stories that children listen to and then read through themselves as they click on the mouse and turn over the pages. If children have difficulty using the usual mouse, there are special large sized ones (which are more like a ball) to help them master the skill. This can develop their confidence and skills in using technology. Ziptales (for early readers) contains very simple stories that have colourful images and characters which engage children. If you are not familiar with it already, you may want to check it out.
LiteracyPlanet teaches children aged 5-15 the fundamentals of reading, spelling, comprehension, grammar and phonics. The site characters are cute and funny. There is a prize wheel for completed work which children love to spin to win a prize. They design their own Avatar with the coins they make from completing work and they always have opportunities to repeat activities they may have struggled with.