What is meant by lower class boy and middle class measuring rod?

This was a phrase that was coined by Albert K. Cohen in
his 1955 publication Delinquent Boys. In that work, Cohen examined
subculture theories as they related to criminality and delinquency. He studied young men
who lived in economically disadvantaged neighborhoods but who were judged by standards
used to judge more affluent groups of young men in higher socioeconomic classes. Critics
of this study argued that you were not comparing apples to apples, so to
speak.

In other words, when people come from different
socioeconomic backgrounds, it is impossible to determine similar causes of delinquency
because the individuals have access to very different levels of economic support. Lack
of money for some individuals is a determining factor for delinquency and further
criminality.

Crime and Criminology/Reid/p.
129