Since my oldest is 14 it is time to select a high school. There are many different options that people choose. I find that most people decide on a public high school or some type of cyber school. We did not exhaust all options but we did try to evaluate four different schools. Choosing a high school can begin in 7th grade or earlier if they have lower grades. Applications can vary on deadlines but be sure to check if there are discounts offered for applying early.
One thing that I would strongly suggest is taking practice entrance exams or even courses designed to help with learning how to take the exams.
Good luck with your endeavors.