Because colleges do not ask about accreditation of homeschooling programs, I recommend that parents consider accreditation only if their homeschooler will be returning to institutional high school. In that case, they should get the high school's promise in writing that course from school X will apply for a diploma. To check out an umbrella school, homeschooling parents should ask questions and not take the literature at face value. Above all, homeschooling parents should ask for references. They should speak with several currently enrolled families.
Umbrella schools provide invaluable services to some homeschoolers.
I suggest beginning with an area your teen finds intriguing. If your son or daughter is interested in medicine, volunteer at a hospital or in a veterinary clinic. If your children love Shakespeare, see if local community drama groups need backstage help. If you have an outdoorsman on your hands, talk to local conservation and sporting groups. Once they begin working, count their effort as part of the curriculum.