A group of children from Manorfield Primary School, Stoney Stanton played this game.

D.H and N.L. said:

To win follow these rules:
If there is one left take it.
For $2$, take both pieces.
If you face $3$ counters and it is your turn you have definitely lost.
If there are $4$ counters left, it is essential to take $1$.
For $5$, take $2$ instead of $1$.

S.W. took these ideas further and came up with some instructions for how to win from the beginning of the game:

The idea of the game is to take the last $1$ or $2$ pieces to win. This ancient game has a theory.

If you go first you can win each time, however when you go second, it depends on what your opponent does for his/her first move.

Go first:
Take $1$ piece, then if your opponent takes $1$ piece, take $2$ pieces to win.
If your opponent takes $2$, (after you took $1$) then take $1$ to win.

Go second: If you go second, then it all depends on what the first person does. If your opponent takes $1$ piece, then you might not win. If your opponent takes $2$, then take $2$ pieces to win.

Well done! I wonder whether anyone can explain why these ideas work?