Excel 2007 : How do I make a line graph out of some complex data that aren't neccesarily numbers

Hi guys, was wondering If you could help me. In school nowadays we need lots of different ways of tracking how children perform (bureaucracy mad!) and I was wondering if you could help me.

Basically I have lots of children, and in the large spreadsheet it says how they are performing in terms of levels throughout the academic year, ranging from September through until July.

They are graded from 1c, to 1b, to 1a, and then so on until they reach 5c, 5b and finally 5a. 5a being the best, what is expected of a very good child when they leave school.

What i want is a way of showing these in a graph of ALL the students throughout the year, I've crudely drawn it in paint here: http://i.imgur.com/VmfIA.png

This would allow us a visual way of seeing how kids have performed. Has anyone any idea how on Earth i could do this? I've played around for ages with line graphs in Excel and can't get close. Here is a copy of a fake version of the spreadsheet, obviously can't upload the real one! http://www.2shared.com/document/hbo_...erexample.html

Any help would be very very appreciated.