Teachers shepherd children through so much more than the ABCs. They encourage and mentor them to be kind and thoughtful to one another, to show respect for adults, and to reinforce good sporstmanship, work ethic, etc.
May is typically when parents and students offer some type of Teacher Appreciation to their hard-working teachers. Sometimes a practical gesture like a gift card is fitting while other times you might want to do something a little more personal. Much of it depends on the relationship you & your child have with the teacher.
Each year has had a different "flavor" for our family and probably is the same with yours.
I've got a friend who has gifted her children's preschool and elementary school teachers with a Bible Quilt Journal as a token of appreciation and support at the end of the school year.