Problema con widgets flutter

Buenas.

Estoy empezando con flutter y para hacerme con el estoy haciendo un 3 en raya, tengo un widget que hace de tablero y dentro de ese tablero creo 9 widgets token que son los que tienes que pulsar y se transforman en un circulo o en una X.

desde el widget tablero le paso al token el estado para poder saber que imagen tengo que poner pero el problema es que se me cambian todos los tokens en lugar del que pulso.

He intentado asignar keys pero no he obtenido mucho resultado. A ver si vosotros podeis echarme una manilla o al menos guiarme por donde tengo que tirar y ya investigo yo.

Tablero:

class Board extends StatefulWidget {
  @override
  _BoardState createState() => _BoardState();
}

class _BoardState extends State<Board> {

  List<int> _score = [0,0,0,0,0,0,0,0,0];
  int _player = 0;
  bool _started = false;
  bool _finished = false;

  bool checkWinner() {
    return true;
  }

  void startGame() {
    this._started = true;
    this._finished = false;
  }

  void finishGame() {
    this._finished = true;
  }

  void tokenPressed(int index) {
    if(this._player == 1) {
      setState(() {
        this._player = 2;
      });
    }
    else {
      setState(() {
        this._player = 1;
      });
    }
    this.doPlay(index);
  }

  void doPlay(int index) {

  }

  void showWinner(BuildContext context, int player) {
    showDialog<void>(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            content: Text(
                'Congratulations player $player, you have won this match.',
                style: TextStyle(
                  fontFamily: 'Dosis',
                  fontWeight: FontWeight.bold
                )
            ),
            actions: [
              FlatButton(
                child: Text(
                    'OK',
                    style: TextStyle(
                      fontFamily: 'Dosis',
                      fontWeight: FontWeight.bold
                    )
                ),
                onPressed: () {
                  Navigator.pop(context);
                },
              )
            ],
          );
        }
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.fromLTRB(0, 50.0, 0, 0),
      padding: EdgeInsets.all(10.0),
      child: GridView.count(
        crossAxisCount: 3,
        children: List.generate(9, (index) => Token(
          index: index,
          player: this._player,
          started: this._started,
          finished: this._finished,
          onTokenPressed: this.tokenPressed,
          onStartGame: this.startGame,
        )),
      ),
    );
  }
}

Token:

class Token extends StatefulWidget {
  final int index;
  final int player;
  final bool started;
  final bool finished;
  final dynamic onTokenPressed;
  final dynamic onStartGame;

  Token({Key key, this.index, this.player, this.started, this.finished, this.onTokenPressed, this.onStartGame}) : super(key: key);

  @override
  _TokenState createState() => _TokenState();
}

class _TokenState extends State<Token> {

  Widget _image;

  @override
  Widget build(BuildContext context) {
    this._image = SizedBox( width: 96, height: 96, );
    if(this.widget.started) {
      if(this.widget.player == 1) {
        this._image = Image(image: AssetImage('assets/circle.png'), width: 96.0, height: 96.0);
      }
      if(this.widget.player == 2) {
        this._image = Image(image: AssetImage('assets/cross.png'), width: 96.0, height: 96.0);
      }
    }
    return GestureDetector(
      child: Stack(
        alignment: Alignment.center,
        children: <Widget>[
          Container(
            margin: EdgeInsets.all(5.0),
            decoration: BoxDecoration(
                color: Colors.white,
                border: Border.all(color: Colors.black),
                boxShadow: [
                  BoxShadow(
                      offset: Offset.fromDirection(0.25*pi, 2.5),
                      blurRadius: 2.5
                  )
                ],
                borderRadius: BorderRadius.all(Radius.circular(10.0))
            ),
          ),
          this._image,
        ],
      ),
      onTap: () {
        if(!this.widget.started) {
          this.widget.onStartGame();
        }
        this.widget.onTokenPressed(this.widget.index);
      },
    );
  }
}

Gracias de antemano.