Tattie Bogle,

IMO, no history of contemporary songs in the USA could be complete without "The Wheels On The Bus'.

But based on my experiences working in after-school programs with elementary school aged children 5-12 years},"The Wheels On The Bus" isn't usually sung as a "back of the bus song" because it is viewed as being a "song for babies" {pre-school aged & younger}.

As I undestand the term, "back of the bus songs" are sung by school aged children who are taking school/camp/church etc sponsored extra-curricular 'field' trips.