Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_13815 ( "School" text, "Mascot" text, "School Corp." text, "Size" real, "IHSAA Class (Football)" text, "Year Joined" text, "Other Conferences" text )

### Question ###
What school corporation has a mascot of Bruins and joined in 1971?

### Accurate SQL ###

SELECT "School Corp." FROM table_13815 WHERE "Year Joined" = '1971' AND "Mascot" = 'bruins'