From what I have read in other threads, it's not an easy process. Not only do you have to get the form, you must either have a doctor sign it if it's for health reasons or state that it is against your religion. Then, the form has to be notarized. It's still not clear to me how often you have to do it. Only once, once a school year? Every 2 or 3 years?
Perry EO worked to make it easier by allowing online optout forms. etc.