The FileMaker Server Technical specifications can be found at http://www.filemaker.com/ce/products/fms/tech_specs.html
Basically you can have 250 FileMaker Pros connected for regular Server and there is no theaoretical limit of FileMaker Pro clients that can be attached to a FileMaker Advanced Server. But there are lots of practical limitations including your network, bandwidth, latency, etc. Also, you can design a database to work poorly with just 5 users if you design poorly. But if you design your schema well, you can have hundreds of simultaneous client connections. My personal experience is that FileMaker does best serving between 10 and 100 users simultaneously. If you get beyond 100, it is important to design efficiently.
One more comment... Will Students and Parents be connecting via FileMaker Pro clients? Probably not. They might be using FileMaker Go. But I assume your'e developing a Custom Web Publishing (PHP) or Instant Web Publishing solution. The easier to implement Instant Web Publishing does have a limit of 100 and only works on Server Advanced. Custom Web Publishing supports up to 200 users.
Thank you for your reply,
Well, we are actually thinking about instant web publishing but considering the limitations of 100 users it will not be suitable for our school since we have over 2000 students which means more than 100 user might be accessing our database at once or even more than 200. Would that mean that we need to look at a diffrent solution or is there anyway around this?
You might want to build a front facing web application based on LAMP (PHP/MySQL) that all of your students and parents use.
You could then use filemaker via ODBC/ESS to create a backend "admin" panel allowing you to run reports and gather data in filemaker.
Customer Web Publishing does support 200 users and this is simultanous users. That would be the best FileMaker way to do things. But as Mike Beargie points out, an inexpensive Lynux/Apache/MySQL/PHP (e.g., "LAMP") can be put together that would easily handle that volume and FileMaker easily does ESS with MySQL so it feels like almost like the MySQL tables are native FileMaker tables. If you want better performance from your FileMaker side of things, you can run the Web Services, PHP and MySQL on the same machine as the FileMaker. Obviously the more you push these different services, the better it is to separate them into different machines. But I run quite a few small business systems running FileMaker with Web Services, PHP and MySQL on the same box. I've only done it on Mac Servers, but Windows Servers will work well too. And doing this will get you around the 200 user limitation. Apache/PHP/MySQL can server VERY large numbers of users simultaneously and your only real limitation will be your bandwidth/latency.
PS: Another advantage of using MySQL is that most web developers will know how to connect PHP to MySQL, but few know how to connect to FileMaker.