The so-called web movement is the invention of former National director John "Spider" Harris in the 1970s. For a full description of web movements, the best source is Tim Hill's document. In a web movement with an even number of tables, as we have here, a section is split into two sub-sections each comprising half of the tables. The second of these sub-sections is boarded "backwards" which is the insight that Spider Harris came up with to make the movement work.
This is how the movement unfolds for one four-table section:
|Four Table Web||
|Table 1 (N/S 1)||E/W 1 playing boards 1,2||E/W 4 playing boards 3,4||E/W 3 playing boards 5,6|
|Table 2 (N/S2)||E/W 2 playing boards 3,4||E/W 1 playing boards 5,6||E/W 4 playing boards 1,2|
|1-2 Bye-stand||boards 5,6||boards 1,2||boards 3,4|
|Table 3 (N/S 3)||E/W 3 playing boards 1,2||E/W 2 playing boards 5,6||E/W 1 playing boards 3,4|
|Table 4 (N/S 4)||E/W 4 playing boards 5,6||E/W 3 playing boards 3,4||E/W 2 playing boards 1,2|
|3-4 Bye-stand||boards 3,4||boards 1,2||boards 5,6|
Of course, as you can see, you need two sets or "cases" of boards (i.e. twelve boards in all). That's the drawback to the web movement (and the reason directors have never really liked to use it until recently). Now, however, that we have dealing machines available, it becomes much less of a burden for the director (or teacher in this case) to set up a web movement.
The other advantage is that, once the boards are put into position, the movement pretty much runs itself. Some of the other alternative movements require changing the movement half-way through, having relays, and so on. These can be somewhat problematic when the players are relatively new to duplicate bridge.
So, as you can see, the web movement isn't only for large single sections, as typically used in tournaments in New England. It can be used any time the number of boards in play is insufficient to cover all the tables in a section.