When I teach Ks 3 (yr7s and 8) about puberty in science this is the basic order we do it in if it helps.
Body changes in males, females and both
So you can start off with how are boys and men different and how are girls and women different. And then you can talk about how / why those changes happen
Male reproductive system
We label diagrams and talk about the function of each part.
Female reproductive system
Again labelling diagram and talk about each part.
Menstrual cycle
Common misconceptions - "I know when girls start their period but when do I?" from boys and also "Why can't they hold it in and just go in the toilet, leaking blood is disgusting". Of course most of us have full control of what goes on with body fluids in that area by 11 so when you think about it the question makes sense.
Gametes
We draw and label the specialised cells and their adaptations for the sperm and egg (this is revision from work earlier in the year). We write about the journey of the sperm cell through the male reproductive system and same for female if the egg is unfertilised
Sexual intercourse
This is done very matter of factly as we are focusing on the science (blood flows to the penis and makes it larger and rigid, it penetrates the vaginas, the couple move and the friction makes the man ejaculated, millions of sperm are released which travel to the egg, only one sperm can break into the egg, the egg is fertilised). There are some fab YouTube videos not showing sex and penetration but the 'great sperm race' which students tend to like. Relationship stuff is done with their PSHE lesson but I always throw in a bit about consent.
Fertilisation and implantation
How a baby develops and what happens at each stage
Infertility, IVF
We don't cover miscarriage or still birth at all but quite often students will ask during this lesson often because it's happened in their families but not really talked about so I address it factually, this is a tricky lesson for alot of students or many will share proudly that they are an IVF baby and what that means
Contraceptives
Different types, benefits and disadvantages
STDs etc are addressed later in their school journey