Hi, I think you would have to visit the school and ask them about their 11+ prep, you can't tell from a website.
There is another thread on this recently, other posters with good local knowledge recommended a number of local primaries, I think Copford was one, West Bergholt? I would search for this and check out all suggested.
Other indies in the area are Holmwood House, Littlegarth, then if you are prepared to go out of town a bit there is Ipswich school, Maldon Court Prep.... it depends on where you want to live too.
As others have said, a prep school is not necessary for grammar school prep, you can use a tutor or even DIY.
Even if you do choose a prep school, you may still need a tutor and quite a lot of the preparation still needs to be done at home and the child has to be willing to do it and have the apptitude for it.