A Revolution in Education
I teach special needs preschool. We are having ours installed 18" off the ground and we will also be using "retired" exercise steps (these are plastic, lightweight and rounded edges) for the students to step up on. Also, I think there are pointers that can be used to simulate the human hand to extend the reach. If not, use a soft tip pointer and then you touch for them. Those are easy to make with pencil top erasers and a dowel rod.
I had it installed 24" from the floor and then for even the smallest of children they can reach up 2/3rd of the Smartboard. I also have a bench next to our Smartboard for children who want to get higher. I do move the tools down to the bottom when my students are drawing on the board. This allows them to use all of the tools.
I teach to children from 6 to 10 so I had to choose a middle height so for shortest children I use a little step bought at the Ikea or pointers.
Hope it helps.