A1 - Two-way prepositions
“Wo” (where, in a stationary sense) takes the dative, “Wohin” (where, in the sense of movement) takes the accusative!
Students have been learning this basic rule for TWO-WAY PREPOSITIONS since time immemorial, and you too will soon realise why you would say “Ich bin in DER Schule,” but “Ich gehe in DIE Schule” for “I’m at school” and “I’m going to school”. Why? Our teacher will explain it all to you.
As always, directly from a classroom in our language school in the heart of Vienna!