When does learning something new become usable knowledge?

I gave the first unit math test awhile ago.  This year we are adding on a six point test to each unit.  It is alligned with the state standards and we hope for improvement on the WKCE.  I felt that the students would know the vocabulary pretty well from our unit, so didn't really "teach" to the test.  Out of 24 students, only 5 students passed (more than 1 wrong isn't passing).  So, I thought, what does a reflective teacher do?  I put students into groups to investigate one of the terms (multiple, prime, composite, array, etc.) and had them present and teach the class.  We posted them in the hallway.  I made up another 6 point test to give right away, but forgot to do it.  So, I reviewed with students this week.  This time 10 students passed.  But, 15 improved their score by at least 1 or 2 points.  And, I had to wonder, how many times does a student need to use a term/new vocabulary word before it becomes usable and meaningful to them?  And, why am I so quick to assume that because I presented the word, or students worked with the word, or knew the meaning once, that s/he will have retained it over a longer time, or put this into usable or retrievable storage?  This reminded me to never assume that I could possibly overpresent vocabulary in any subject area.  The good from all of this is that, even though the unit has passed, I will continue to find ways to bring back those terms (and others) throughout our math year.