In primary school, I think there is little point in teaching children about the organelles of a cell or Darwinian evolutionary theory. They simply are not yet equipped to understand or evaluate any of these things in a truly scientific way. Instead, what matters the most is observation. Only when they know how to observe will they know how to account in theory for what is observed.
In my imagination, the ideal primary-school biology teacher is a Lakhota brave teaching the students to observe and identify organisms in nature. He takes them outside and expects them to pay close attention to what they see, hear, and smell. If they see tracks of an animal, they mark well what it is they observe and what it might mean. They draw and write about some of the plants they encounter, and they also keep in mind whatever they have come across, because the teacher will test them both during and after a trip. A student finishing primary school might well say, ‘I don’t know what mitochondria are: I have never seen any in real life. But I can tell apart Eastern and Western Meadowlarks by their bird calls, because I have seen and heard both, and taken notes about the sound that each of them makes. Can you tell them apart?’