"Did you walk to school this morning?"
Translation:Ar shiúil tú ar scoil ar maidin?
Sometimes ar translates as “to”, e.g. Bhí siad ar dinnéar againn. (“We had them to dinner“).
It’s not necessary for ar maidin in this sentence, given the past tense of its verb. Another way of expressing “this morning” is ar maidin inniu.
Why isn't the correct translation: "Did you walk to school in the morning?" ? I don't see where "this" comes from.
If you want to be specific about referring to "this morning", the Irish is ar maidin inniu - ar maidin seo is considered béarlachas.
But unless context or tense implies otherwise, ar maidin is read as "this morning". If you are clearly talking about a day in the past, or using the habitual present or past tenses, "in the morning(s)" makes more sense.