BTW, I had a good hands-on day today, and I thought I'd share what we did since you were asking about it. This was not in any book or curriculum that we used. We just figured it out.
DS8 was getting a bit confused in his "Key To Algebra" lesson today, which involved isolating the variable and solving for X. If the problem was 6x + 4 = 2x, say, he was having trouble understanding that he needed to subtract 6x and not add it.
We pulled out the blocks. A big red block was used to represent X; a big blue block was used to represent -X, and little natural blocks were plain old numbers.
We put down a pencil to divide the problem at the = sign. On one side we placed 6 red blocks and 4 natural blocks and on the other side we placed 2 red blocks. He could then see that adding 6 red blocks wouldn't help because then he'd have 12 red blocks, not 0.
Instead he pulled out 6 blue blocks to "neutralize" the red ones, and used them on both sides of the pencil, leaving 4 blue blocks, or -4x, on one side and 4 natural blocks, or the numeral 4, on the other side.
It really helped him to see the concept. If words don't seem to clarify, blocks or drawings or something hands-on often do.
HTH!