CREATE TABLE table_51259 ("Name" TEXT, "Years" TEXT, "Gender" TEXT, "Local board" TEXT, "Suburb" TEXT, "Authority" TEXT, "Decile" TEXT, "Roll" FLOAT)

What year was the name mount roskill grammar school?
SELECT "Years" FROM table_51259 WHERE "Name" = 'mount roskill grammar school'
SELECT "Years" FROM "table_51259" WHERE "Name" = 'mount roskill grammar school'