I remeber in HS we did a burn test on various nuts to determine caloric content. Weight nuts, burn em and the re-weigh(cashews are highest btw) and you could do the same thing for coffee showing how length of roast lowers caffine content. Unfortunatly i have no idea how one goes about detemining caffine quantity in a seed pit. Somebody on this forum is sure to know.
You can make layered lattes to show thermal differences and how liquids of differing temp/densities mix.
Not sure how the parents feel but you can test memory/retention for caffinated v. non caffinated students by playng a game of concentration.