thanks for your advice, really appreciate it.
I've had a look at other open source SISs and haven't found something that looks user friendly, easy to install, etc.
There doesn't seem to be much activity going on at http://sis.akedu.us/, I've already had a look at http://www.schoolforge.net/education-software/web-based-student-information-systems-sis and didn't find anything that looked like it was simple or useful enough, maybe there is a gem in there somewhere. I've just installed Schooltool on Ubuntu, it looks simpler and easier than all the rest I've looked at so far, but I couldn't find the attendance feature yet and it doesn't use PHP or MySQL
On the Filemaker side of things, I'm told it can be set (one of the advanced versions of Filemaker I think) to use MySQL as a backend database, PHP as a scripting language etc. Not sure exactly how it works but it's supposed to be very fast to develop web applications with (Point & Click, Drag and drop etc).
Cheers,
Barry