I don't think it is 'naughty' to flexi-school, in fact it is becoming more and more common for a very wide variety of reasons. It can help to calm difficult children, develop a closer parental relationship, and can be particularly useful for children who are 'different' from the normal academic ability range of their class.
That is like saying it is 'naughty' to put your child in a top Indie Prep or buy lots of resources and books... as it confers some advantage educationally.
Unfortunately the reality for many state Primaries is that with the best will in the world, crowd-control, rather than individually stretching children, takes over the most part of the school day.
If parents have the time and wish to spend a day or two 1-1 with their child, why look down upon it?
The only advice I can give on spellings is that grammar has an 'a' not an 'e' before the r. Common mistake - I once saw a tuition centre advertising 'Grammer School tuition' on a large expensive banner
There are many spelling programs in book, CDROM, and Internet form to purchase - I would look at them and decide what works best for your child if this is a weakness.