So I’ve acclimated to the kanji vs kana usage being a bit inconsistent across different example sentences. Sometimes an example will throw in a higher-level kanji, afterwards you might see it in kana form under a different vocab item.
However, I just found a single example sentence that treats the same kanji both ways:
This has got me wondering what’s producing this strange behavior.
I suppose it might even be intentional, given that 学 is coming up on the very next level (5). “Let’s see if they can pick up on it a bit early if we show them the reading then the kanji,” or something like that.
Would be interesting to know what’s going on in any case.