I’ve got into the terrible habit recently of starting every article with “… is a much neglected area that really needs more attention”*, but with something as important as thanking I really really think it’s true:

Teaching thanking (articles and worksheets)

* apart from my articles on first and second conditionals, where I started both with the warning “there is a danger that the sheer number of fun activities for these points will make you spend far too much time on them”