CREATE TABLE table_13525 ("School" TEXT, "Location" TEXT, "Mascot" TEXT, "Enrollment" FLOAT, "IHSAA Class" TEXT, "# / County" TEXT, "Year Joined" FLOAT, "Previous Conference" TEXT)

What year joined had an enrollment less than 438 and an AA as the IHSAA Class?
SELECT "Year Joined" FROM table_13525 WHERE "Enrollment" < '438' AND "IHSAA Class" = 'aa'
SELECT "Year Joined" FROM "table_13525" WHERE "Enrollment" < '438' AND "IHSAA Class" = 'aa'