I’m not sure if high-school economics classes get to the point of discussing them (when I worked and at an economics and finance themed high school, the topic never came up, which may mean something), but if one somewhere does, than here is a Cultural Literacy worksheet on the concept of a mixed economy.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.