Is she or isn't he?

Our exchequer leghorn that hatched in May - is she a pullet or is he a cockerel? We had thought it was the latter. But he hasn't grown much of a tail and this morning we found a white egg in the henhouse where he roosts. Admittedly, two white leghorns are among the birds in the same henhouse but they gave up laying for the winter about 3 weeks ago. So, is he actually a she? At the moment we just don't know but the signs seem to be pointing to pullet rather than cockerel.