You've received great information from previous posters.
I'll just add one thing, and that is a tip for parents to check a test's website.
You may already have explored the MAP test website (NWEA.org), and may have read their articles about sharing test results, using score ranges, utilizing three pieces of data (triangulation) to make placement decisions etc. The downloadable RIT score charts also provide interesting background information.
The website provides a page of resources for Parents and Students (link-
http://www.nwea.org/resources-parents-and-students) and a page about assessments (link-
http://www.nwea.org/products-services/assessments). Information is freely available to the public and accessible to all.
You may wish to follow the links and find the demonstration of how the test works and what a test-taker will experience while interacting with the test. Navigation on the website to get to the assessment demonstration went something like this, there may be other paths as well:
products & services
assessments
MAP for Primary Grades
Testing Details
Watch a demo