This is a very old folk song. I present here the Scout version and a published version -- you will understand the difference. This song is structured like the 12 Days of Christmas, in that it builds as the verses progress, until at the end, the singers respond with all 12 lines. It is not sung to a "stock" tune -- you will have to find someone who knows it to learn the tune. Here is how the Scout version begins:

Leader: I'll sing you one ho
Group: Green grow the rushes ho, What is your one ho?
Leader: One is one and all alone and ever more shall it be so.

That is the basic form. Here is the second round:

Leader: I'll sing you two ho
Group: Green grow the rushes ho, What is your two ho?
Leader: Two, two little Cub Scouts, Clothed them all in green ho
Leader and Group: One is one and all alone and ever more shall it be so

So, you can see how it goes. Here are the other 10 lines:

Twelve for the Twelve Apostles
Eleven for the eleven who went to Heaven
Ten for the Ten Commandments
Nine for the night (nine??) bright shiners
Eight for the April rainers
Seven for the seven stars in the sky
Six for the six proud walkers
Five for symbols at your door
Four for the Gospel makers
Three, three the rivals

According to "Rise Up Singing" published by Sing Out publications the song was first printed in "English Country Songs" by Broadwood and Maitland in 1893. Here are the lyrics:

One is one and all alone and evermore shall be
2, 2 the lily white boys, clothed all in green-o
3, 3 the rivals
4 for the Gospel makers
5 for the symbols at your door
6 for the 6 proud walkers
7 for the 7 stars in the sky
8 for the April raiders
9 for the 9 bright shiners
10 for the 10 Commandments
11 for the 11 that went up to heaven
12 for the 12 Apostles