one of the things (beyond that they are free) that I like about the Schoolexpress units is they have LOTS of information in them. Information that it's easy to use as is, or to supplement if necessary. They are parts were the lad can dictate answers, and parts where he has to use his brain and his own fingers to do the answers.
Pages to colour (not that the lad likes to colour), pages to draw (LOVES drawing), fill in the blanks and what not. Good smaller unit studies.