I have been using Lexia for Secondary students with Nessy being used at our primary. It has a good evidence base and works out around £25 per/pupil per/year. They have updated their system this year and its now called PowerUp Literacy – much more engaging for older learners and they can work fairly independently through the programme. Recommended time is at least an hour per week but as its available online at any time it can also being used for homework/independent learning.
Lloyd.