Repeating decimals may be introduced in a mathematics education long before any other infinite series or the methods used to tame them, such ass limits.

I see the introduction of a conceptually incomplete notion as one of the big hurdle of school-level math: without limits, children are asked to just adopt the axiom that there is such a thing as a concept of infinity with any form of practical usefulness, and this riles.

It's only with limits and proper formalism that I was reconciled with maths that frankly were just tending towards approaching an equality with bullshit.