The law has recently changed:

The child receiving home instruction takes a nationally normed standardized achievement test published or normed not more than ten years from the date of administration and administered under the conditions as set forth by the published instructions of the selected test and by a person qualified in accordance with the test’s published guidelines in the subjects of reading, language, mathematics, science and social studies. The child is considered to have made acceptable progress when the mean of the child’s test results in the required subject areas for any single year is within or above the fourth stanine or, if below the fourth stanine, shows improvement from the previous year’s results;

There are a couple of significant changes here. First is that parents may administer tests
to their own children AFTER May 23, 2016 if the publisher allows. Second, and more important, is the change from requiring a child score at the 50th percentile or better to the 4th stanine.

Stanine is short for standard nine. The name comes from the fact that stanine scores range from a low of 1 to a high of 9. For instance, a stanine score of:

1, 2, or 3 is below average
4, 5, or 6 is average
7, 8, or 9 is above average