It’s usual for Prep schools to start preliminary discussions about senior choices in Yr4. If your school hasn’t raised the issue yet, I would ask for a meeting with the Head, because now really is the time to be thinking about this. Many key open days have already happened early this term.
A key thing people are paying for with Preps, is….prepping. This involves advice and guidance to parents about options and routes, as well as prepping the children for entrance processes. So make sure you are getting this info.
I’m sure that given you’re on a full bursary, next stages and funding of them have always been on your mind and this isn’t really the first time you’re thinking of it.
As has been said, many schools now test in Yr6 even for entry at 13+. It is called pre-testing. Some will offer a bursary/scholarship to a linked Prep from 11+ if starting at 13+, which could be a boarding Prep. Some will give a bursary for your child to continue in their current prep, although probably not if they already have a full bursary until 13.
The fact they already have a full bursary is probably a recommendation, as usually these are only given even at Prep stage to very academically able children.
Yes, you need to decide if you want day school or boarding and to transfer at 11 or 13. Full bursaries can be available to any of the following, but it is true, that larger schools with historic foundations often have more funds available. Your Prep Head should know this stuff, especially as a Head of a 13+ school, who must be sending students on at 11 and 13 to both day and boarding.
Lots who board from 13 seem to recommend boarding from 11 in a Prep that is a boarding Prep. That’s something to consider.
If you need several meetings with your Head, just ask and push if needed to get the advice you need. Visits in person to schools are on again, so you should be able get some tours to help you decide and Bursars at the senior schools will usually be very happy to discuss your precise financial circumstances and be honest about what could be available.
All the best….sounds like a bright future.