This was the first cardboard divider I made. It is in an old sand table I inherited when I took over a new classroom. It is a metal square and less than a foot off the ground. (I actually liked it because it was simple and allowed me to build and add my contraptions to the table. There was only one problem: it would not hold water. If I wanted water in a table, I had to have a second table. My room was small, so I ended up getting one table that would hold both sand and water.
The cardboard divider is very easy to make. Take two flat pieces of cardboard. Cut the pieces so they fit into the table. Next, make slits in the middle of each piece approximately equal in length. One piece is slit from what will be the top and the other is slit from the bottom. They are then slipped together at the slits. Tape the joint that is made by the intersection of the two pieces of cardboard and then tape it in the table.
These spaces can facilitate some focused individual play.
Or provide another space into which a child can transport or collect objects.
The running joke in the room is that this apparatus is preparing the children for the world of work with each of them toiling away in their own little cubicles. You be the judge.