I played elastics growing up in Montreal early 70's and we played this all the time but we did it differently. We did 0 to 9 ( I think - that was a long time ago) and each number had a different step to it. 0 was you just jumped over it, 1 was you jumped and landed on both strings, 2 you put one foot under and one over on the first side and then switched. Does any of this sound familiar to anyone? I'd like to teach it to the students in my classes.