Public school students need to be taught the true origins, histories and meanings of many American holidays, festivals and observances, no matter how ugly they may be.
For example, students should know that Memorial Day originated with African American slaves.
There are a lot of accomplishments of and contributions to American culture and society by African Americans and other Americans of color that are/were omitted from school textbooks and ciriculums. Students should be taught about this stuff also.
For example, public schools don't teach students about the contributions of the Tuskegee Airmen during WWII.
A lot of students don't know about Bessie Coleman, the first female African American airplane pilot, and her contributions to aviation.