Academic progress could be improved further in some centres by teaching pupils in narrower age groups, as there were "limitations" in grouping the whole 11 to 16 age range together.
They said teachers could remind themselves that not all children are at the same stage by taking steps like calling the register in birth order rather than alphabetically and grouping children together by age.
The bureau calculated and cross-referenced lifetime earnings for each major and each career field by grouping survey respondents into eight age buckets consisting of five years, determined the median annual earnings for each age group, multiplied the number by five, and added the totals together.