We investigate differences in the teacher-learner interactions in Reception, Year 2 and Year 4 science and literacy classrooms through three measures: (i) the proportion of open questions asked by the teacher, (ii) the rate of successful responses, and (iii) wait-times. A regression analysis of data from 20 schools and 102 lessons suggests that classrooms in socio-economically disadvantaged areas offer distinctive patterns of interaction, i.e., typically associated with those approximately two years younger in the more affluent school districts. We then closely examine the quality of two contrasting dialogues from reception science classes of schools in poor and affluent areas. We see how teachers' questions can work or fail to work to achieve the expected quality in scientific dialogue, and thus how effective use of open questioning might be indicative of quality. In conclusion, we discuss quality of talk as an explanation of class differences in learning outcomes of schooling. (Contains 6 figures and 1 table.)