How to test English vocabculary range of students?

select 300-500 words or terms RANDOMLY from the dictionary.
Should included about an equal amount of nouns, verbs, adjectives,etc
then use a format like multiple choice question,
give 4 different definitions for students to choose.
only one answer can be the correct meang of a vocab.
then calculate the score in percentage,
that percentage would be the vacabculary range of a student.

I suggest you arrange a scrabble competition.

There are a number of ways to test the vocabulary of students:

1) Set up a vocabulary test, by selecting not random words from the dictionary but choose words that you believe are suitable for the children of the age you're testing (also remember, like the person said above, to have a well-proportioned amount of the different parts of speech e.g. noun, verb, adj etc.)

2) Provide a story or piece of writing and use specific words that you believe that the children should know or is suitable for testing vocabulary. This method also comes with a multiple choice reading comprehension test that consists of not only the questions that define a certain term but questions that will test if the students understand the whole phrase or sentence.

Some examples:
why did the author use "this phrase" here?
When the author said "this phrase" what meaning was he/she trying to imply?
What is a synonym for "this word?"
Use "this word" in a sentence

I personally think the second approach will be more effective since I believe vocabulary is not solely based on how many definitions you know or remember but how many words you actually understand and know how to use.

Hope it helps =)