You can adapt these based on your relationship and the occasion:
"You make learning fun and exciting every day. We are so grateful for the kindness and guidance you provide." buying teachers presents
"Thank you for being such a patient and inspiring teacher! I've learned so much because of you." You can adapt these based on your relationship
"Hi everyone! A few of us are coming together to get a group voucher for [Teacher's Name] to show our appreciation. If you'd like to contribute, please let me know by Friday!" please let me know by Friday!"