There are many nationally standardized tests available for homeschoolers, but the Woodcock-Johnson has many features which set it apart.
Most standardized tests are grade specific "bubble" tests-- timed, multiple choice tests where your child chooses the right answer and fills in the bubble. The Woodcock-Johnson is different in every way. First, it is not administered in a particular grade. A professional test administrator starts your child at a level which will be easy for them and lets them work their way up till they can no longer do the work. They can go as high as they are capable with no regard to their grade. This is great for kids who excel in at least one of their subject areas. Most of the Woodcock-Johnson is not timed. (There are timed portions if the test administrator uses them, but I do not, unless the parent orders that portion in addition to the 9 batteries I already give.) By not having a timer going there is much less stress involved for the student. Slow students are not penalized for being slow. Their score reflects their knowledge, not their speed.
The Woodcock-Johnson is also great for kids with reading difficulties, including bright younger children who have knowledge in other areas which out passes their reading, such as math, social studies, or science. The only areas of the test which the student must read totally on their own are the reading portions. Therefore, their reading ability does not affect their other subject scores in a negative way.
Kids with any learning disabilities or attention issues find the WJ much easier to take. Each battery is finished within 15 minutes and a very different subject (which starts very easy) begins, thus resetting the child's attention "clock." I have worked for years with kids with autism, ADHD, ADD, dyslexia, and much more.
The best part of having your children take the WJ is the feedback the Mom gets. Most standardized tests send results in the mail several weeks after testing. Many times the reports are full of numbers and information which are difficult to understand. The WJ administrator has the ability to score your child as they test and take notes on their strengths, weaknesses, learning styles and much more. I set down with parents immediately following testing and give them all of my notes, the computer results of the test, and explain all of the above.
Normally it is priced only slightly more than other standardized tests, the convenience, reduced stress, and accuracy of the Woodcock-Johnson make it an exceptional tool for homeschool parents to help them know how to educate their children in the best way.