private bool DoesThisEmailExist(Teacher aTeacher)
        {
            List <string> emails = new List <string>();

            aTeacherGateway = new TeacherGateway();
            emails          = aTeacherGateway.GetAllEmails();
            foreach (string email in emails)
            {
                if (email == aTeacher.Email)
                {
                    return(true);
                }
            }
            return(false);
        }