Search for a placement test and you get PDFs. They are free, and they are fixed: the same forty questions for every child, marked by you at the kitchen table, producing a recommendation that a particular publisher’s Level 4 is about right.
That last part is the problem. A publisher’s placement test exists to sort your child into that publisher’s books. It is a sales instrument doing double duty, and it is why two of them can put the same child two years apart.
A fixed test also cannot follow a child. If question three is too hard, the remaining thirty-seven are all too hard, and what you learn is that they struggled — not where they actually stand.