Angular 4 - Post Checkboxes from an array

I am trying to print checkboxes from an array with a checkbox, to later

        <table>
          <thead>
          <tr>
            <th>class</th>
            <th>subjects</th>
            <th>class speaker</th>
          </tr>
          </thead>
          <tbody>
          <tr *ngFor="let class of classes">
            <td></td>
            <td>
              <div class="form">
                <input type="text" class="md-input-text" placeholder=" " value=" " [(ngModel)]="subject"/>
                <label class="md-desc">subjects</label>
              </div>
            </td>
            <td>
              <div class="md-checkbox">
                <input type="checkbox" id="" [(ngModel)]="checkBoxValue"/>
                <label for=""></label>
              </div>
            </td>
          </tr>
          </tbody>
        </table>

Unfortunately, if I check one of the checkboxes, everyone of those will be checked too. Any idea what I am doing wrong?