Of all the singing groups at St. Theresa’s, the Adult Choir rehearses and performs the most. The Adult Choir starts in late August and continues to late June. In addition to singing the 9:30 AM music three Sundays each month, The Adult Choir is called upon to sing special Masses, such as First Communions and Confirmations; sings for several of the extended services relating to high holy days; and has participated in the Billerica Ecumenical Choir fest since its founding eighteen years ago.