there's no logical way that it should all be done in an hour....not for second graders.
that's asking too much and the enjoyment of teaching it is going to run right out of time.
have them make it a two day thing and let the teacher and principal know, .....they must guess that, already...

good luck...
I've done projects with all of the lower grades and for a classroom to do what you plan is headed for disappointment.

actually, there is a way to do it......

I got all comfortable in bed, fluffed up my pillow, was warm and began to think about your situation

you can imbed the tiles, pieces, whatever is going onto the little terra cotta pots, by the method first used in ancient times..

have sanded grout all ready to smear on the pots, then add the pieces for the pot and there you have an ancient "memory jar"...
I saw one a really long time ago and it just popped back into my head, thinking of the fastest way to have a project done in a short time..

do a google 'image' search and type in 'mosaic memory jars'..
you should find the one I saw a long time ago...

now, I feel better and am headed back to bed....lol

g'nite

yep, the premixed grout and adhesive all in one is your only option

I did one in BSchool one year .(that is what got me started) It said to use mastic put it on and imbead the tile or what ever you are using on it.It work good for that pro..I have since learned so much sice then .

Memory jars as so very cool as well. Take some pics!

My mother in law has one that she made years ago. I think she used something called "Putty" to stick hers on a galvanized bucket. She had all kinds of fake jewels, jewelry,cracker jack toys, buttons, pins, marbles, just about anything you could think of, she has on that bucket. I want to make one too and actually have started saving "junk" to put on mine.