Clearing the DataGridView and re-populating it

I've been trying to figure out how to clear and redraw the DataGridView. But so far I have been getting the same results where the data just keeps on writing and writing itself on refresh, resulting on redundant records.

Here is my code:

DataGridView1.DataSource = Nothing
    DataGridView1.DataMember = Nothing
    DataGridView1.Columns.Clear()
    DataGridView1.Rows.Clear()

    SQLSTR = "SELECT * FROM '" & ClassIntl & "'"
    DBConn()
    SQLDA.Fill(DS, "Grades")
    SQLCONN.Close()
    DataGridView1.DataSource = DS
    DataGridView1.DataMember = "Grades"
    With DataGridView1
        .RowHeadersVisible = False
        .Columns(0).HeaderCell.Value = "Student ID"
        .Columns(1).HeaderCell.Value = "First Name"
        .Columns(2).HeaderCell.Value = "Last Name"
        .Columns(3).HeaderCell.Value = "Quiz 1"
        .Columns(4).HeaderCell.Value = "Quiz 2"
        .Columns(5).HeaderCell.Value = "Quiz 3"
        .Columns(6).HeaderCell.Value = "Quiz 4"
        .Columns(7).HeaderCell.Value = "Quiz 5"
        .Columns(8).HeaderCell.Value = "Quiz 6"
        .Columns(9).HeaderCell.Value = "CS Prelim"
        .Columns(10).HeaderCell.Value = "CS Midterm"
        .Columns(11).HeaderCell.Value = "CS Finals"
        .Columns(12).HeaderCell.Value = "Attend Prelim"
        .Columns(13).HeaderCell.Value = "Attend Midterm"
        .Columns(14).HeaderCell.Value = "Attend Finals"
        .Columns(15).HeaderCell.Value = "Exam Prelim"
        .Columns(16).HeaderCell.Value = "Exam Midterm"
        .Columns(17).HeaderCell.Value = "Exam Finals"
        .Columns(18).HeaderCell.Value = "Total Prelim"
        .Columns(19).HeaderCell.Value = "Total Midterm"
        .Columns(20).HeaderCell.Value = "Total Finals"
        .Columns(21).HeaderCell.Value = "Final Grade"
    End With

Suggestions would be great, thank you!