At foundation level there is virtually no difference between the exam boards.
The higher papers (grade 4-9) have more differences but they’re all similar enough that revision books etc are published for all exam boards.
edexcel is the most popular particularly at foundation as it is less wordy than some others.
there are three papers, two calculator one not. So learning to add subtract multiply and divide without a calculator doesn’t get you much more marks.
getting very familiar with your calculator and how to use it is a good way to pick up marks. Most schools have a calculator they recommend and there’s a lot of videos on corbettmaths or similar on how to use it.
for example it can work out averages, has an equation solver you can use for algebra etc etc.
There’s lots of videos on YouTube eg this one
but in all honesty it’s best done little and often- so have it every maths lesson and use it every maths lesson.
most schools will also do mock analysis so your child will have been given a list of topics from the last set of mocks - those he got right (green) those he got partially right (amber) and those he got wrong (red)
the idea is that if he/his tutor work on the amber questions or the easier questions that he should have got right he can hoover up more marks.
rather than doing topics that are beyond him.
the papers in general go from easy to hard so any red questions early on are worth focusing on,