Datesweeper (months and dates game)
Draw a 5x5 (or 4x4 or 6x6 etc.) grid on the board and fill in each square with a random date. Secretly choose one of the squares to be the "mine" but don't tell anyone (except maybe the HRT ). Split the students into groups and decide the order of the groups. Have the students janken ; the winner of the group chooses one of the dates and says it in English. If the square is safe, replace the date with a number indicating how far the "mine" is. If the square has the "mine", that group must do a batsu game, and the board will be refreshed with a new "mine" location .
I've decided that "4/20" will contain the mine. (Example is bold for the sake of explanation.)
Group 1 chooses "10/31". Since 4/20 is a maximum of 4 squares away, I replace it with the number 4.
Group 2 chooses "2/14". It is a maximum of 2 squares away, so I replace it with 2.
Group 3 chooses "5/19". It is a maximum of 3 squares away, so I replace it with 3.
The grid now looks like this.
If you have any crazy smart kids, they might figure out that:
-Based on "4", the mine must be in the first column (because otherwise you would have written 1, 2 or 3).
-Based on "3", the mine must NOT be in the fourth row. With the two pieces of information , it must be 12/5, 8/14, 4/20, or 5/5.
-Based on "2", the mine must NOT be in the fourth column (which should be obvious once they figure out the pattern for the first two). However, since the number is 2 and not 1, the mine is NOT 12/5 (which is 4 away), NOT 8/14 (which is 3 away), and NOT 5/5 or 7/26 (because they're 1 and 0 away, respectively). Therefore the mine must be in 4/20, so that is the square that they must not say to avoid the batsu game.
Although it's not unlikely that you might have some kids who will figure out the mine location right away, the focus should be on saying the dates and enjoying watching the class clowns do silly batsu dances, rather than logicking the game to death. (Although if you really wanted to, you could probably adapt it to higher levels using a much larger grid and having the students compete in pairs, like battleship.)