In my class the children may choose to work at a table, on a floor mat or at a mini table. These mini tables are great for when you don't have much space in your class [as with mine]. The children also use them when they have been working on a floor mat with a piece of material and then wanted to write up the work they are doing on the floor.
I actually find that the children prefer these mini tables then the big tables and they seem more relaxed and better able to concentrate on the floor. I love that Montessori gives children this freedom. In the picture above I have three tables stacked. In the picture below one of the new children is doing addition at a mini table.
If anyone is wondering where to get these tables from: they are just regular bed tables.