One major way they're keeping costs down at SLOCA is by leasing space at an unused facility that saw its past life as a public elementary. Now the district wants that space, so they'll have to find other digs.

Privates also tend to pay their staff less, in both wages and benefits. This is a major reason why they hire teachers with lower credentials and/or less experience.

In addition, the privates in my area that are similarly-priced have large fund-raising activities, demand a certain number of parental volunteer hours as part of the price of tuition, and also have some hidden costs that are passed on to parents throughout the year.