7places for the first letter, 6 places for the second etc, that's 7!
but s and o are duplicated so if you don't mind double counted combinations are 7!=5040
If you count SchoOls, schoOlS, SchOols and schOolS (using capitals to show the two different o's and s's) Then because there are four duplicates for every combination we have to divide this number by 4.
5040/4 = 1260 non duplicated arrangements.