C# Scoping Question

My problem is that I have 2 different forms and in 1 form I have an empty listbox, and in the other form I have the user input information that copies an object and goes into ArrayList. I can't access the ArrayList in the other form, where I have my listbox. Here is the code:

namespace StudentScores
{
      
      public class MainForm : System.Windows.Forms.Form
      {
      
            public System.Windows.Forms.ListBox mainList;
            
            private System.ComponentModel.Container components = null;

            public MainForm()
            {
                  
            
                  InitializeComponent();

            
            }

            protected override void Dispose( bool disposing )
            {
                  if( disposing )
                  {
                        if (components != null)
                        {
                              components.Dispose();
                        }
                  }
                  base.Dispose( disposing );
            }

            #region Windows Form Designer generated code
            ///
            #endregion

            [STAThread]
            static void Main()
            {
                  Application.Run(new MainForm());
            }

            private void btnExit_Click(object sender, System.EventArgs e)
            {
                  this.Close();
            }

            private void btnAdd_Click(object sender, System.EventArgs e)
            {
                  AddStudent newStudentForm = new AddStudent();
                  newStudentForm.ShowDialog();
            }

            public void FillStudentListBox()
            {

ERROR -->      foreach(Student s in students) // Compiler says that students cannot be found
                  {
                        mainList.Items.Add(s.DisplayText());
                  }
            }
      }
}


namespace StudentScores
{
      
      public class AddStudent : System.Windows.Forms.Form
      {
            ArrayList students = new ArrayList();
            
            private System.ComponentModel.Container components = null;

            public AddStudent()
            {      
                  InitializeComponent();
            }

      
            protected override void Dispose( bool disposing )
            {
                  if( disposing )
                  {
                        if(components != null)
                        {
                              components.Dispose();
                        }
                  }
                  base.Dispose( disposing );
            }

            #region Windows Form Designer generated code
            ///
            #endregion

            private void btnCancel_Click(object sender, System.EventArgs e)
            {
                  this.Close();
            }

               // I want the listbox to be populated with students ArrayList content
            private void stuAdd_Click(object sender, System.EventArgs e)
            {
                  Student stu = new Student(txtName.Text, txtScore.Text);
                  students.Add(stu);
                  this.Close();
            }

      }
      
}

// This is my Students Class File
namespace StudentScores
{
      /// <summary>
      /// Summary description for Student.
      /// </summary>

      public class Student
      {
            

            public string Name;
            public string Scores;

// constructor
            public Student(string name, string scores)
            {
                  this.Name = name;
                  this.Scores = scores;
            }

            public string DisplayText()
            {
                  return Name + ", " + Scores;
            }
      }
}

Any ideas on how to solve this problem?