We're having our exam in PSEP next week and I'm tasked to deliver the closing remarks for a graduation but don't know how to prepare this kind of speech.
Keep it short and simple. People want to get going! Everyone will be very emotional, so you can be sweet and even corny. It will be the one time you can get away with it! Say something nice about the class, as a whole or as individuals.
Once somebody searched for a citation which could apply in any given situation, whether it be happy or sad, the end of something or the beginning thereof. The response one person offered was, "This too, will pass." This means of course that the only unchanging thing in life is change itself. Graduation is an event commemorating the transition of life from one stage to the next (thus all the "pomp and circumstance") but the lessons learned at school (and not necessarily those from the books) will serve someone for the rest of his life. Circumstances change, even friends separate, but one's experiences gleaned throughout these years somehow remain and influence one's future choices.
Another idea is to take the word 'education' and expound upon its true meaning. If you look at it etymologically (starting from the end and working backwards) , it means 'the state or condition of leading out':
-tion: the state or condition of
-duc-: to lead
The idea is that to truly educate someone is not to make him or her conform to your own ideas but to teach that person to think for himself. I think you could make a good speech just from that.
A final suggestion: I heard a superb speech once where the orator used the example of the child's toy which bounced back upright no matter how many times you tried to knock it over. (You know, they were old-fashioned doll-like toys with a rounded bottom and were usually bears or clowns). You could use this as a springboard for a speech about tenacity and will, and the fact that success need not always be mesured by superlative performance but by simple perserverance in the face of adversity and resilience (or the coined word for it - 'boucebackability.')
All the best for your speech! I hope I have at given you at least one idea you find useful.