SFO SCHOOL AND I-20 VISA (San Francisco)

Hi friends,
We are an spanish family moving to San Francisco for one year's sabbatical arriving there during the summer. Now we are searching for school for our 4 kids (4, 10, 13 and Protected content we have many problems to find places in schools provided with the I-20 visa document. They have no place or are too expensive. Any idea about how to procede?
Thanks a lot and best regards.
Diego