LANSDALE, Pa. (CBS) – Students sent a retiring Montgomery County teacher off with style and song. North Penn High School students in Lansdale wanted to show their appreciation to Sue Cassel.

Cassel has been an avid supporter of the school’s theater department.

A big surprise for Cassel, who is a huge ABBA fan as the students belted out songs from the school’s musical “Mamma Mia.”

They say they wanted to congratulate her and “thank her for the music.”

Watch the video above to see Cassel’s sendoff.