Networking – How to Restrict Computer from Connecting to Outside Wireless Networks

My application requires a private connection between client computers and a server computer locally. The client computer shouldn't be allowed to connect to outside wireless network.

To be clear, the question is how to prevent client computers from connecting to outside network.

I'm thinking of two options:

1. Use (or write) a software that do the job, i.e, a software that requires account/password for every new wireless connection. It's similar to parent-control software. Unfortunately, at the moment I couldn't find such software. Do you have any suggestions for this?

2. Use a guest account on client computers, but I'm not sure if it's feasible.

Any help please?

Here's the application: A local exam for classroom.

The classroom is fully equipped with LAPTOPs (Windows XP/7); 1 for teacher and n for students.

The (student) computers must be connected to a server (teacher) to feed questions and (possibly) be graded. The (student) computers and teacher computer are on a local LAN network.

The students is not allowed to connect to outside networks. But it's not just "not allowed", because I have to prevent such things happening (prevent students connecting to outside). Otherwise, they could connect outside and Google the questions.