CREATE TABLE table_13815 ("School" TEXT, "Mascot" TEXT, "School Corp." TEXT, "Size" FLOAT, "IHSAA Class  ( Football ) " TEXT, "Year Joined" TEXT, "Other Conferences" TEXT)

What school corporation has a mascot of Bruins and joined in 1971?
SELECT "School Corp." FROM table_13815 WHERE "Year Joined" = '1971' AND "Mascot" = 'bruins'
SELECT "School Corp." FROM "table_13815" WHERE "Mascot" = 'bruins' AND "Year Joined" = '1971'