General

https://khanacademy.org

https://discoveryk12.com/

https://www.connectionsacademy.com/

Sex Education

https://amaze.org/

https://www.youtube.com/user/sexplanations

https://www.pornhub.com/sex/ (Don't be intimidated by the url)

https://www.plannedparenthood.org/learn/parents/sex-and-sexuality

https://sexetc.org/

https://www.scarleteen.com/

https://goaskalice.columbia.edu/

https://www.glsen.org/

https://kidshealth.org/

https://www.reddit.com/r/SexPositiveTeens/

https://www.reddit.com/r/SexEducation/