Do you have to be certified to teach in a private school?
It depends on the school's policies as a rule. Generally a school will make it very clear if certification is required in the first instance. Often a school will hire you provisionally if it feels you can meet the state certification eligibility requirements within a reasonable length of time. In the long run you will be well-advised to get certified. Most states will require evidence of a bachelor's degree and a background check before approving a teacher hire in a private school. But, apart from that minimum requirement, most state education authorities take a hands off approach. The bottom line is that private schools can hire whoever they wish.
What a private school is really looking for are teachers who can teach. Research has shown that good teachers are professionals blessed with superb verbal abilities. Put another way, they know how to communicate their subject extremely well. That has little or nothing to do with certification.
Coming in right behind superb verbal abilities is experience. A private school principal will value these two attributes far more than he will mere teacher training or education courses.
Is there any evidence to suggest that certified teachers are better teachers?
According to the Abell Foundation's report Teacher Certification Reconsidered: Stumbling For Quality there is inconclusive evidence. In my opinion teacher certification is a concoction of the political-educational establishment to protect, shield and justify the inadequacies of public education. After all the state education office only looks at transcripts and required courses to determine if certification standards have been met.It never actually watches a teacher teach.
This is why private schools value a teacher who is passionate about his subject more than they value teachers who are certified to teach a subject. Yes, the private school principal will look at your transcripts, but what he will really focus on is results and your ability to be a great teacher.
A degree in your subject is important.
You have to know your subject. Most upper schools will value strong tertiary level credentials highly. A master's or a doctorate in your subject is an excellent door-opener. The ability to teach Advanced Placement or International Baccalaureate level courses is also another big advantage. In academia, a bachelor's degree is only the first step in your educational journey. Go for the doctorate while you can! Possessing that terminal degree puts you in an elite group of educators who have worked extremely hard to earn that degree.
Offer specialist certification.
Special education, guidance counseling, curriculum development, vocational education, media specialist - these are specialist areas which are much in demand. While not in the same league with a terminal or a master's degree, subject certification shows that you have explored methodology and current practice in your area in some depth. Assuming you keep up those certificates updated, you will contribute much of value to your chosen academic community.
Demonstrate that you have integrated technology into your teaching.
Using a tablet PC and an electronic whiteboard effectively are essential skills in the classroom these days. Communicating via email and instant messaging are givens. Private schools have been in the vanguard of educational technology since the mid-'90's. Understanding how to use technology effectively in your teaching is not something certification has even begun to address and measure.
Offer teaching experience.
If you have taught for 3-5 years, then you have worked out most of the kinks. You understand classroom management. You have figured out how to truly teach your subject. You can connect with your students. You have learned how to communicate with the parents. Experience counts far more than certification as a rule.