L.H.
I am a veteran homeschooling mom. A lot of the curriculum out there have placement tests. Math courses and reading almost always have placement tests.
I use McCall-Crabs for reading comprehension. My son reads a short story and answers questions and it gives me his level of understanding. To me just reading words isn't a good indicator, comprehension is key. I use Math U See for both kids and they have placement tests on computer for free. If you're just wanting an overall read on ability I'm sure there are tests out there for that.
Please know one of the beauties of home education is you can work on strengths and weaknesses without a child feeling inept. My son is an auditory learner. His memory is incredible. He struggles with language arts because it doesn't make sense to have rules and then many exceptions to every rule. He excels in math because the rules stay the same. He always finishes his math coursework earlier in the school year and loves it. I've been able to put some pieces together that makes his language more interesting.
If you'd like to visit more about anything homeschool, please feel free to pm me. I'd also encourage you to find a co-op of some kind near you. The support, experience and encouragement you'll receive will help you in this journey.
Blessings!
L.