Beck, McKeown, and Kucan, authors of Bringing words to life: Robust vocabulary instruction (2002), devised a "three tier" vocabulary system.

TIER ONE - basic words, such as the, who, and when
TIER TWO - academic words that apply across the content areas, including tragedy and community
TIER THREE - specialized words are abstract words which apply to specific content areas, like osmosis and diffusion, which both apply to science.

Check out this podcast for a fun way to learn tier 3 vocabulary words! It is especially helpful to auditory learners!

Just Vocabulary podcast

In the video linked below, Dr. Judy Montgomery evaluates a student's tier vocabulary skills. See how she examines his knowledge using the Montgomery Assessment of Vocabulary Acquisition (MAVA). Although the link appears to be an advertisement for the MAVA system, it is still informative and shows a basic outline of one type of assessment.

http://www.youtube.com/watch?v=765KlgPNo7Q