There is still much controversy about the mechanism of the development and evolution of life, even if the history of change from non-living matter through very simple lifeforms through increasingly more complex lifeforms is gaining wider acceptance.
In one camp there is the claim that life can be explained solely in terms of changes brought about through chemistry and physics, while in the other camp there is the claim that the increasing complexity of life actually contravenes the laws of physics, and that some additional mechanism is necessary to explain this increasing complexity.
In both camps a strong religious/non-religious undercurrent plays a part, with the people in one camp believing everything can be explained completely in terms of the forces and energies observed in the laboratory and/or accepted by standard science, with those in the other camp believing that the physical observed universe is just one aspect of a greater cosmos.

Students in elementary school and in the early years of post-elementary school should not be embroiled in the controversy of this unsettled question (the question of mechanism, not the question of history) at such an early age, and they should just hear the history of changes that life has gone through, leaving discussion of the mechanism and other controversies related to the evolution of life to some later year in high school, when the sciences related to lifeforms and their nature and evolution are introduced.

The aim in presenting the material at first to children in elementary school should be to paint the overall picture in broad strokes (rather than getting mired in minor details and technical explanations), and again video and graphics would be the most useful tool. The study of the origin and evolution of life on earth in elementary school and the early years of post-elementary school could include the following:
- the early earth (between 4.6 billion years ago and 4.1 billion years ago) before life began,
- early unicellular lifeforms in the oceans between ~ 4.1 billion years ago and ~ 1.7 billion years ago, and the evolution of all subsequent lifeforms from these primitive early forms,
- increasing oxygen levels in the oceans and microbial mats,
- increasing complexity in unicellular organisms,
- evolution of sexual reproduction in primitive organisms,
- first multicellular organisms around 1.7 billion years ago,
- the emergence of animals in the oceans around 550 million years ago,
- the diversification and growth in size and complexity of animals in the oceans,
- the appearance of the first vertebrates,
- the increasing levels of oxygen in the atmosphere through photosynthesis over ~ 3 billion years,
- the migration of lifeforms onto land edges bordering the seas, and the adaptations that were necessary,
- the spread of plant and animal lifeforms over the earth's surface,
- the continued diversification and evolution of lifeforms,
- since life began, 99% of all species have become extinct,
- the development of a soil layer,
- mass extinctions,
- the age of dinosaurs from ~250 million years ago to ~65 million years ago,
- the evolution of flowering plants ~130 million years ago,
- the evolution of insects,
- the evolution of mammals and their diversification and rise to prominence after the mass extinction of the dinosaurs ~ 65 million years ago,
- the origin of primates ~55 million years ago, their subsequent evolution and diversification,
- the origin and evolution of humans,
- diversity amongst the 10-14 million species of life presently on earth,
- the future of life on earth, including questions about the future of humans, and the question of life elsewhere in the universe.