In The Process of Education (1960), the American psychologist Jerome Bruner argued that any subject can be taught in an honest form to children at any age, if it is introduced at the right level and revisited later in greater depth. This is the spiral curriculum: a course returns to central ideas several times, each time deeper than the last.
Principles - Revisit. Key ideas such as fractions, narrative or the scientific method come back, not just once. - Build. Each return adds complexity and connects to what has been learned. - Start from the big ideas. Choose the concepts that matter most and keep them in view. - Check. Each visit begins by finding out what is remembered.
Why it can work Revisiting content spaces out practice, which research on memory supports; see the forgetting curve and the review of spacing by Cepeda and colleagues (2006). Returning to an idea also lets children connect it to new knowledge. See making connections.
In practice - Maths: counting, then adding, then place value, then fractions, with each stage revisiting number. - Science: forces in primary school, motion in lower secondary, then Newton's laws later. - Literacy: stories first as listening, then as reading, then as analysis. - History: a topic visited briefly and then in depth.
Cautions - Shallow repetition. If each return repeats the same level, children are bored and learn little. Make sure the content grows. - Gaps. If a child has not mastered an early stage, later visits will not fix it unless the foundations are rebuilt. Combine with checks like those in mastery learning. - Time. Return visits take lesson time; decide what to leave out. - Evidence. The idea is well supported in principle, but direct evidence for entire spiral curricula is limited. Treat it as a design principle rather than a guarantee.
For parents: when a topic seems to come round again, it is probably meant to. Ask what is new this time. If the child says "nothing", mention it to the teacher.