I'm 15 and this week my class is going to teach sex education: How to have sex and how to be safe (I guess they are going to show us how to do it too). Now I want to know: Should I join the class on that day or not?
"Say: Are they equal those who know, and those who do not know?" (39:9)
I would advise that you go to the class and seek appropriate information from your masjid/Sunday school about Islamic views of sex.
In sex education classes in secular schools, the emphasis is generally on basic anatomy (of men and women), sexually transmitted diseases/infections, and preventing pregnancy. They do not teach you "how to have sex". If you are fifteen-years-old, and you do not know the definition of sexual intercourse, how a woman becomes pregnant, or what a menstrual cycle is, I would advise you speak with your parent/s regarding this.
The information covered in the class on basic health is important information for every human being who has reached puberty in order to care for themselves and for others. When you attend the class, I advise you to have the correct intentions, namely to understand human biology for the sake of appreciating the marvels of the human body that Allah has created and to prepare you for marriage one day, inshaAllah.
In a masjid/Sunday School setting, you should have the opportunity to learn the other part of "sexual education", specifically the morality, emotional, and Islamic aspects related to marriage. If you are too embarrassed to seek knowledge about this from a person or are afraid someone might shame you, perhaps ask for a book recommendation on Islamic marriage.
I encourage you, as a fellow Muslim, to observe chastity and have sexual relations within the bounds of marriage only as commanded by Allah, and to have proper intentions when attending such classes. A side benefit of attending secular sex education classes in high school is that the knowledge you learn may very well encourage you to remain on the sirat al mustaqueem as you realize that even the "safest" sexual acts may still result in unwanted pregnancies and diseases.
I think, you should. If teenagers don't learn basic sex education, maybe they will have problems in the future such as genital infections, unprotected sex acts. Basic sexual aspects must be learned at school only, not on Internet or with parents! Very good opinion about this problem i found there: https://ask.naij.com/education/should-sex-education-be-made-compulsory-in-schools-i23980.html - read 1st answer.
i think, go there, but: 1) do not look at images/views of naked humans, also generally do not look at women and girls at your school. 2) do not believe to information that is given in atheist lections and atheist books, if they do not have strong proofs. the information for school pupil probably does not have proofs with them. for example , they teach that sex without marriage is ok and that masturbation is ok and that using contraceptives (condoms etc) is ok. do not believe that.
(Use of physical contraception (Condoms etc) is permitted in Islam only in few cases).