Singapore has a placement test on the website to let you know what book to order, and the books are by the half-year (2A, 2B, 3A, 3B, etc.)
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My children are using Timez Attack for multiplication tables and division facts this year. There is a placement test when you first create a user, so that known facts are not drilled.
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We are using Click N Spell. There's a place on the site where you can look at a list of all the spelling words. You could quiz him on them and figure out what lesson to start (it does not do this automatically -- wish it did). I did this with my child who'd rather be challenged than perfect, and moved him ahead to the point where he missed a word.Â
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We use Rosetta Stone. That's grade-independent.
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We use Getty-Dubay for writing. I would think handwriting skill would vary widely within a classroom anyway. You can view sample pages to figure out what book to start in.
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I think you'll find that homeschooling is super flexible. If you can't look at something ahead of time and you find out it's too easy, you can send it back or sell it. If it's too hard, put it away and buy the book before it.
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