One test to determine grade level

Schools often pay ridiculous sums of money for such tests. If Khan Academy would have such a test, then I could say let's save money and use it instead. 

Right now I've assigned my grade 8 students the first few levels of grades Mastery courses to determine their weak points, but it takes far too long. To achieve mastery they have to take the Course challenge multiple times to get close to mastery of 80-90%. Grade level 1 (annoyingly titled Early math) takes some kids so long and some of those questions just don't seem like grade level 1 math. 

So, please make a single test to determine their grade level knowledge. I could then begin there, instead of the beginning. I could argue that we ought to use Khan Academy for everything math related. I might even be able to argue, if the school adopted it, to donate, rather than waste money on much more expensive and less useful programs.

Thank you.