Also make sure you have set teh checkboxoptions. This object tells the grid what to consider true and what to consider false for this cell.
this.gridControl1[1,1].CellType = "CheckBox";
this.gridControl1[1,1].CheckBoxOptions = new GridCheckBoxCellInfo("1", "0", "", false);
this.gridControl1[1,1].Text = "1";
this.gridControl1[3,1].CellType = "CheckBox";
this.gridControl1[3,1].CheckBoxOptions = new GridCheckBoxCellInfo("True", "False", "", false);
this.gridControl1[3,1].Text = "True";
If this is not the problem, is this a GriddataBoundGrid or a GridControl you are using?