dd is taking the glos exam which is also CEM.
You don't need a tutor.
But you will need to spend some time checking they have everything they need.
I have 4 books, for the 4 sections of the test
Verbal Reasoning
Non Verbal reasoning
English
Maths
We have gone through eg the maths book and checked that she knows all the subjects. eg, she wasn't familiar with some terms 'prime factors' for example threw her. as did Mean Median and Mode.
But because she is fundamentally bright, and the concepts have already been taught, it has been easy to polish up her maths vocab to cover all the bases.
times tables are essential, drill them if necessary, as division facts as well as multiplication facts.
Same with English.
Non Verbal Reasoning is mostly a case of practising, so they get the idea of all the different types there are.
Verbal Reasoning has 21 question types. Many are straightforward - find the synonym or antonym for example, some less so. Get a book, work through, do one page as explanation and then do next page of same type against the clock. Getting their eye in over the little tricks they use is important.
Looking at words which have more than one meaning, and finding synonyms and antonyms is good practice.
Which brings me to the last thing. Speed and exam technique.
He needs to practice working as fast as he can.
Exam technique - things like how long to spend on a question before giving up, to always put an answer (sensible guess) don't leave it blank. To use the answers you have to help (eg, multiplying an even number, the answer can't be an odd number so ignore any answer choices with an odd number)
Over the summer do 1 or 2 'mock' exams, under exam conditions, to practice all of the above (be careful though, if he gets a bad mark, it may be worth not disclosing that to him, it doesn't mean he will do badly on the day)
Finally, stress that grammar schools are great, but so are other schools, and it isn't the end of the world if he doesn't pass, at the same time, you will be proud of him for giving it his best shot.