dEhiN wrote:What's the difference in meaning or grammatical analysis in the two? I don't know any Irish, but I'm curious.
They basically just use different prepositions; no difference in actual meaning, outside of the one dialect area (where one refers to speech, the other to writing). as is a preposition that's often use to express origin or medium (it's the preposition used when saying where you're from, or that something is made out of something). It's often translated as English 'out of', though I've gotten into the habit to try to avoid translating prepositions outside of specific contexts as it just leads to me trying to map them semantically one-to-one.
i just roughly corresponds with English 'in'. My guess is teachers think i nGaeilge sounds too Englishy, and so avoid it, despite it being common among all native speakers (mostly because teachers never interact with actual native speakers and generally have an atrocious level of Irish, even the Gaelscoil teachers).
I hope that answered your question!