"Thank you for being such a patient and inspiring teacher! I've learned so much because of you."
"To celebrate the end of the year, we're putting together a small gift from the whole class. No pressure at all, but if you'd like to join in, we're collecting [Amount] each." "Thanks for helping me grow!" "To the best kind of teacher—thank you for everything." "Thanks for being an inspiration this school year!" What Teachers Actually Value buying teachers presents
You can adapt these based on your relationship and the occasion: "Thank you for being such a patient and inspiring teacher