IXL Learning, Prepdog.org and Mr. Anker Tests offer third grade common core math and language arts practice tests, as of 2015. Practice tests are also available at SoftSchools.com and Eduplace.com.
IXL Learning offers math practice tests in numbers and comparing, division, place values and mixed operations. IXL's language arts tests assess third graders on sentence types, sentence structure, synonyms and antonyms.
Prepdog.org has practice tests on common core subjects that include geometry, measurements, numbers in operations and algebraic thinking. Mr. Anker Tests has assessments on reading comprehension, spelling, vocabulary and Roman numerals.
SoftSchools.com features practice tests on numbers, patterns, integers and probability. Houghton Mifflin's Education Place features practice lessons that improve students' test taking skills.