Display posters using
Widgit Symbols
This is part of the display by Samuel Pepys School, St Neots, Cambridgeshire, (a specialist school for cognition and learning), which children prepared ahead of my visit.
The display uses Widgit Communicate In Print symbols (for making symbol-supported printed materials), which can be obtained here: Widgit Symbols.
This excellent display may give you ideas for a similar display in your school.