Not sure of the norm for your area, but anything will be appreciated.
I used to teach PreK, and always liked gifts from the kids (i.e. a homemade card, something that they picked out, etc) and a note from the parents. I was usually given a gift card in conjunction, which with finances being tight was greatly appreciated.
One year I had a 4 year old student use money from her piggy bank to pick out a gift for me and then she made me a card. It wasn't anything fancy, but it was so cute and touched my heart. I used the post it notes from it, but two years later I have the other portion on my desk. So cute.