The first verb my students learn, sein (to be) is also the most irregular verb in German. (Similar story in English...) Actually, I haven't taught students regular verb endings yet, so they don't know just how irregular sein is, but they do know there isn't much of a pattern. And so we have come upon one of the hard truths of language learning:
Some things just have to be memorized.
It isn't particularly complicated, nor is it very exciting; it just takes some time and effort. I try to offer a variety of ways for my students to practice.
We start with guided notes:
We use Quizlet:
and Learning Apps:
Another one of the options I have is these puzzle cards.
They contain a variety of subjects and then the different forms of sein for students to match up. I made them using some puzzle shape clip art I got from Teachers Pay Teachers. I printed them out on card stock, and I plan to have them laminated when I get a chance.