Coach Zim,
Well, there are several certifications offered by the USABC that are beyond Level I and II.
Bronze level certification is similar to Level II, but provides more material, more hands-on and talks about how you can profit from the business of coaching bowling. The program has recently been re-written and will last about 18 hours. Four hours on Friday evening, eight hours on Saturday and about six hours on Sunday. You will get a chance to coach volunteer bowlers that are willing to get free coaching from the students in the class (under the watchful eye of the instructor). The new format also emphasizes the use of video to analyze the students.
Beyond Bronze is the Silver level certification. It focuses on the science of bowling such as ball physics and detailed delivery methods for maximum performance.
As fas as High School coaching, you can receive certification from the National Federation of state High Schools (NFHS). It is an eight hour class on the general principles of coaching athletes. I took that class at the end of last year's coaching summit. Good class. However, it was one of the toughest exams I have ever taken. You are given six months to complete and turn it in. Now I don't mind exams. I finished my college degree with a 4.0 average. If you were to assign a grade to my NFHS results, it would have been a C-.

Not good for a six-month-take-home-exam.
Here's the link to the USABC page:
http://www.bowl.com/bowl/usa/common/static.html?page=coaching_mainpage It has everything you could possibly want to know about coaching programs.
Hope this helps,