Housing tenure (coded as owned/mortgaged, privately rented, subsidized housing rented from council/housing association), crowding status (coded as a value greater than 1 for the ratio of number of residents to number of rooms in house), maternal educational attainment (coded as no high school qualifications, high school, beyond high school), quintiles of household disposable income [a measure assessing income when the child was a toddler (2–4 years of age)] and accounting for family size and composition and estimated housing benefits 18 and finally parental social class (the highest social class of either parent) at enrolment based on the Registrar General's classification of occupations: I/II (professional/managerial and technical) versus IIINM or lower (skilled non-manual/-manual, semiskilled and unskilled).
