If you want credit for biblical Hebrew courses taken elsewhere, contact the Classical Studies Department Chair. If you want placement so you can continue in biblical Hebrew at William & Mary, talk to the course's professor. That professor will review your records and complete a departmental placement form. You will then submit that form to the Department Chair for final approval. You must request an "instructor permission" override for the course.
Credit for Hebrew at Religious School, Bar or Bat Mitzvah Training
Hebrew 101 is very intensive and covers a lot of material. Your facility with reading Hebrew, and your familiarity with some vocabulary and phrases, will help you at the beginning of Hebrew 101. But even students who have had a significant amount of conversational Hebrew find that they have to work hard at Hebrew 101 after the first six weeks or so. Students who had years of Sunday School Hebrew find that, beyond the first 2 weeks of Hebrew 101, they have to work just as hard as complete novices do. Unfortunately, some prospective students of Hebrew don't realize that. They try to join in the middle of the year, at the Hebrew 102 level. But both the level and the kind of knowledge of the language that they miss by not taking Hebrew 101 make it impossible for them to join the class at that point. This is not a matter of some arbitrary rule, but of the substance covered in the class. I always invite such students to check out my web site and come to class; they always disappear after one class meeting, after they realize how much they would need to catch up on before they would be up to the level of the others.
Credit for Jewish Day School
Even several years at Jewish day schools do not always provide students with the level of knowledge of grammar covered in Hebrew 101 at William and Mary. You should probably start at the 101 level; your familiarity with the Hebrew alphabet, and the vocabulary you have probably mastered, will make it easier for you but not to the degree of being able to dispense with 101.
Please contact the Department Chair if you need more information regarding placement.