This forum discussion gives reasons why some families choose the option of a homeschool umbrella school. 

An umbrella school is generally a private school which has an option available for homeschooling. An umbrella school has students which actually attend the private school, as well as students who are registered as homeschoolers.

An umbrella school is an entity, typically considered a private school, which serves to oversee homeschooling families and help them meet the requirements of their state’s homeschooling laws. Sometimes the umbrella school is an actual physical private school with which homeschooling families can partner. In other cases, an umbrella school is more of an organization established to help homeschoolers comply with the law.

A homeschool umbrella school is an independent school that offers enrolled families a way to comply with state laws. In most circumstances, these schools offer families a chance to homeschool under private school laws, where they may find much more freedom from intervention than following homeschooling regulations individually. These types of schools can be set up as a local organization, or as a distance or online school. In some states, legal homeschooling may only be done through an umbrella or cover school, while in other states, umbrella schools can offer benefits to homeschooling families, but are not required by state law.

There is no universal definition for an umbrella (or cover) school because home education laws vary from state to state. In some states, homeschoolers can get some level of support and legal protection for their home education program. Umbrella schools typically provide legal legitimacy to a family's home education program, maintain attendance records, host field trips and activities, and more. 

An umbrella school is a homeschooling “school” that oversees the high schoolers’ education. Different states have different names for umbrella schools.

At one time or another, many homeschool families examine the possibility of enrolling in an umbrella or cyber school. An umbrella school is a homeschool program operated by public charter schools or directly by regular public schools. 

This forum discussion goes over the pros and cons of using an umbrella school. In some states, there is a requirement for homeschoolers to register with an organization, and umbrella or cover schools offer this.