I followed this and made changes to suit out school system as follows
$periods[] = "Period 1";
$periods[] = "Period 2";
$periods[] = "Period 3";
$periods[] = "Period 4";
$periods[] = "Period 5";
However when it displays it displays like this period1 period2 period1,period2,period3,period4,period5 so there are 7 periods but only 5 lines