I have been attempting to set up a small computer lab in my classroom, as well as provide internet connection to other classrooms in my building. My current diagram is

modem
4 port router
computer1 computer2 computer3 switch
computera computerb computerc

Currently, I've been trying to set up mini labs in other classrooms, but when I use a router in their rooms I get no internet signal. (This is all hardwired, we have no $ for wireless capable PCs). Here's my question: should I be using switches in all cases after the router connected to the modem? Will that router provide security for everything after it?

Thanks!

upluplow, please don't hijack existing threads. I've moved your post to a new thread.

The router should provide some basic security if it is performing Network Address Translation however going further than that will depend on what the router is capable of and how it is configured.

With regards to the upstream PCs not having internet access I would suggest checking that the switch ports provide an uplink capability or ensure that you are using a crossover cable to connect them.