Marlton Mom, any advice is good advice. I have about 2 yrs experience in photography, but I will be the first to admit that I'm no Pro. Any recommendations will be accepting in the spirit with which they are given.

Matt
Hi Matt,
I know that you probably have some experience doing this sort of thing but I'm going to lay it out for all to see as I've done this for 6 years at a school for a million different events.
I'd say that in a situation like this your best bet is to come to the rehearsal that the school will have where they show the kids what to expect and how to behave.
Make sure everybody (Students and Staff involved in the ceremony) understands that you will need the kid to
stop and pose with the diploma long enough for you to take the picture. That would mean having the diploma presented, then having the student and anyone else
STOP, pose the way you want them and SMILE long enough for you to take the picture.
This needs to be
practiced as part of the ceremony otherwise you are screwed! The kids will be flying off the stage and you will only get some shots. Others will be blurry or the backs of heads.
If everyone knows what the deal is then the adult presenting the diploma will help you with the kid that is not in the right position. (You will have to ask them to redirect if needed, the adult won't figure it out because they are not thinking like a Photographer.
The key here is that everyone is on board with the plan and the Stop, Pose and Smile is a part of the drill.
If you can accomplish that they you are golden!
The next deal here is what kind of pose are you after? Do you want a side of the head while the student is being handed the diploma or do you want a more posed shot where they stop and face front.
I have found that this type of shoot does not take long and is not really disruptive to the ceremony. Having everybody aware of what you need is essential and this needs to be communicated ahead of time so the kids practice it when they do their run through.
The one thing you will hear about is the grumbling from parents because you are front and center and they are "missing" the shot with their crappy point and shoots and obnoxiously way underpowered flashes.
It may help to let the parents know that "a photographer" that is "helping the school" will be positioned in front to take pictures which will them be available to the families, blah, blah, blah....
I would have this announcement made at the start of the ceremony since nobody bothers to read the stuff that is sent home. You would not believe the number of people who get extremely pissed at the fact that you are in front and taking pictures and they are not. The Grandparents are going to be the ones that are the most disruptive because they are clueless and frankly they just don't give a damn about being considerate except for when it's their boopsie's turn.
By the way,
Shoot on burst so you get a couple of exposures in case you get the blinkers. 2 in 10 will be blinkers if you just shoot 1 shot. One will look like a mini "cereal" killer and if you're really lucky you'll get the ever popular "finger in the nose" shot. You'd be surprised how many teachers have itchy noses and it Looks like a "finger in the nose" shot but it's not.
Now we come to the group shot. This is the students in class formation and gown posing with their teachers. Again this needs to be practiced ahead of time. If Possible
do it before the ceremony, perhaps at the assembly point for the kids. Now keep in mind doing it before hand is next to impossible because kids are gonna be late and they'll fly in at the last minute. (Side note: This is almost always because Grand Ma/Pa is late or stuck on the toilet and everybody has to come together because Grand Ma/Pa will never find the place.).
So here is how you get around that....
Let's say the ceremony starts at 10 am. Tell people that..... but it really starts at 10:15 so that you will have time to take the group shot right before they go out to the ceremony. The school staff knows this 10:15 is the real time, but whatever you do don't let the parents know, and besides, the line of Grandparents waiting for the bathroom at the preschool will be out the door so everyone could use the extra time.
So let's recap:
1) have the staff and kids on board with the plan of Stop, Pose and Smile during the ceremony. PRACTICE this.
2) Make an announcement before the ceremony that you are up front because you are shooting for the school and remind parents to stay in their seats. (Ha! good luck with that one!!)
3) Take the group shot BEFORE the ceremony, afterwards will be CHAOS!!
4) the real SECRET time that the ceremony starts is at 10:15. The parents think it's 10!
5) Have somebody make sure there is enough toilet paper in the restrooms for all those grandparents! It will be like they haven't gone in a week, trust me!
Ok, so I hope I have helped. I really hope I have made you laugh. If you do enough of this sort of thing you'll find out that everything I've said is true...
~ ESPECIALLY the grandparents! ~
Good luck,
Marlton Mom