I'm getting the following error while saving a record in Student object: "Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger StudentAttendanceTrigger caused an unexpected exception, contact your administrator: StudentAttendanceTrigger: execution of AfterInsert caused by: System.ListException: List index out of bounds: 12: Class.StudentAttendanceClass.StudentAttendance: line 24, column 1"

I have the following objects and fields:
Object 1: Student
Field Name: Name(Std), & Roll_Number__c

Object 2: Attendance
Field Name: Name(Std), Roll_Number__c, Student__c(Master-Detail Reln, Student object is master)

My requirement is when I create any student record, it should create 12 Attendance records (Jan to Dec) in Attendance object. I have written the following Apex class. I'm getting the above error while inserting a record in Student object. Any inputs highly appreciated!!!


public class StudentAttendanceClass
{
public static void StudentAttendance(list<Student__c> StudentsList)
{
list<Attendance__c> AttendanceList = new list<Attendance__c>();
list<string> MonthsList = new list<string>();
MonthsList.add('Jan');
MonthsList.add('Feb');
MonthsList.add('Mar');
MonthsList.add('Apr');
MonthsList.add('May');
MonthsList.add('Jun');
MonthsList.add('Jul');
MonthsList.add('Aug');
MonthsList.add('Sep');
MonthsList.add('Oct');
MonthsList.add('Nov');
MonthsList.add('Dec');
for(Student__c VarS : StudentsList)
{
for(integer p = 1; p <= 12; p = p+1)
{
Attendance__c VarA = new Attendance__c();
VarA.Name = MonthsList.get(p);
VarA.Student__c = VarS.id;
VarA.Roll_Number__c = VarS.Roll_Number__c;
AttendanceList.add(VarA);
}
}
insert AttendanceList;
}
}