All students who attend St. Theresa are taught under the Ontario Secondary Curriculum. From 2002 to 2004, St. Theresa had success rates below 80%, but by the 2007 school year, the success rate had risen to 92%. In a 2012 report from the
Fraser Institute that ranked Ontario secondary schools in terms of academics for the 2011–2012 school year, St. Theresa scored 6.1/10, ranking it 378th out of the 725 Ontario secondary schools included in the report. Out of the other high schools in the Algonquin and Lakeshore Catholic District School Board, St. Theresa Catholic Secondary School received the lowest score in terms of academic achievement, behind
St. Paul Secondary School, which scored 6.8/10. The decline in academics in recent years is a startling one, as St. Theresa had maintained an exceptionally high academic standing in years past, having ranked highest in the school board during the 2010–2011 school year with a score of 8.6/10. Despite this decline, St. Theresa Catholic Secondary School's score was still above the provincial average. The Fraser Institute's results for the 2013 school year noted that STCSS had made significant improvements, rising to a score of 6.7/10, ranking it 273rd out of 740 Ontario secondary schools. In terms of school board rankings, STCSS tied for the lowest score in the ALCDSB with
Holy Cross Catholic Secondary School in Kingston. This score just surpassed the provincial average of around 6/10 and making it the lowest ranking secondary school in the ALCDSB, with the second lowest being St. Paul with a score of 6.8/10. The 2015 school year proved to yield only greater decline, with STCSS scoring 5.7/10 and ranking 415th out of 676 Ontario secondary schools, scoring below the provincial average of about 6.0. It once again was the lowest scoring secondary school in the ALCDSB, with the next lowest score being St. Paul with a 6.5 and ranking 289/676. It tied with
Holy Cross Catholic Secondary School for the lowest scoring secondary school in the ALCDSB, with the next lowest being Nicholson with a 6.2/10 and ranking 371/740. It retained its place as the lowest ranking secondary school in the
Algonquin and Lakeshore Catholic District School Board, with the next lowest being
Holy Cross Catholic Secondary School with 6.3/10. STCSS remained the only secondary school in the ALCDSB to rank below the provincial average. STCSS' score would decline further in the 2018 school year to 5.1/10 and a rank of 536th out of 738 Ontario secondary schools, falling below the provincial average score of 6/10. STCSS was the lowest scoring secondary school in the
Algonquin and Lakeshore Catholic District School Board, with the next highest score being
Holy Cross Catholic Secondary School with a score of 6.2/10. By the 2019 school year, STCSS' score had declined to 3.6/10, falling well below the provincial average of 6/10 and ranking 664th out of 739 Ontario secondary schools. It had the lowest score of all secondary schools in the
Algonquin and Lakeshore Catholic District School Board, with the next highest score being
Holy Cross Catholic Secondary School with a score of 5.9/10. In the 2022 report, St. Theresa received a score of 6.1 out of 10, ranking it 357th out of 689 Ontario secondary schools. This score was below the provincial average of 6.0. == Facilities ==