The best classroom walls aren't wallpaper - they're a rotating reference the whole class can lean on. Change one wall each half-term to match the topic and children start scanning it without prompting.
Anatomy, times tables, world maps and periodic tables sit well as permanent anchors. Around them, rotate posters that match the current unit: rainforest ecosystems, Roman timelines, a poet's portrait.
Print big. A2 is the minimum size we recommend for a classroom wall - anything smaller and the back row can't read it.