Why it's necessary
Browsing donorschoose.org again. Last time I looked, nothing worthy was listed. This time I found a proper 'hands-on' project and funded it. A teacher was requesting funds for something called Rekenrek. Hadn't heard of it, so looked it up... it's just a one-string abacus for mastering addition. Excellent idea.
While looking it up, came across a perfect illustration of what happens when you DON'T learn math with hands and eyes:
That clinched it. Had to buy Rekenreks for this teacher.