It’s outrageously useful for:
Explaining, rubbing out, explaining again
Getting the child to re-write what you’ve just written so they can explain it to you
Leaving extra Ninja Maths homework up on the board
Just-before-bedtime explanations of things like the planets, fractions, a thunderstorm and the difference in speed between light and sound (so you know when it’s time to duck)
Drawing up “Happy Birthday” and adding flowers or robots
Homework planning – e.g. creative writing: who, where, when, why etc
I can’t over-emphasise how essential the home (magnetic) whiteboard has become.