I just googled this and this is what I came up with: www.teachhub.com/spark-class-spirit-tie-dye-t-shirts-project
I have done this with a birthday party but have not done anything at this scale. I would imagine the key would be to have things super organized ahead of time. When I did it at a bday party I had the instructions and bags ready to go. Maybe you could have a check in where you have the kids pick up their t-shirts & bags and have them write their name on the tshirt tag and bag with a permanent pen.
As for supplies maybe you could get a nearby craft store donate some of them in exchange for promoting their business to attendees. Hardware stores often carry RIT dye also, so that may be a business to check for donations. That would be a great spot to get the buckets!
Also thinking that it's best to limit color choices to keep things simple-- school colors?
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