Warm drinks are good.
Lemon juice in water. Lots of lemon!
ACV
Honey is good, too.
Gargling salt water - excellent!
Slippery elm.
Sip water while you are teaching the class.
Projecting from the diaphram, that's right-on advice, too.
Complete vocal rest is best for irritated vocal chords.
If you must speak, then:
Don't whisper! It is TERRIBLE for the voice.
Just talk at a medium-quiet level.