Capital High School is located in the Boise school district and has a very large attendance boundary. Here is a link to their school website which should hopefully answer a lot of your questions:
Home - Capital High School
Ironically, I went to Capital High School for one year (back in 1976-77) before moving out of the country and then ultimately back to Boise.
Many of my clients have had very good things to say about Capital. My 3 sons all went through Mountain View High School in Meridian so it was always kind of odd cheering for my children's teams to beat my high school alma mater in football, basketball and rugby.
A school can only help provide the tools and the direction for it's students. I think the parents and students themselves need to determine how to best utilize those tools and make the best of them. A think a motivated student and family has a better chance to "be educated" at any school vs a non-motivated student at an Ivy League college. The fact that you are taking the time to ask - leads me to believe your family will be do just fine.