A large scale observational study by educational psychologists of 141 UK primary classrooms used a partial interval time-sampling observational schedule to record the frequency and type of verbal behaviour of teachers and whether students were "on-task" (following the teacher's directions) or "off-task" (not following the teacher's directions). Results were analysed and comparisons made between lessons that followed National Literacy Strategy or Numeracy guidelines and those that did not; between schools from different geographical contexts, e.g. rural or inner-city; between classes where there was one, or more than one, adult present; between schools with different percentages of free school meals; and between a.m. and p.m. lessons. A range of findings included higher rates of students being on-task than found by previous studies, and correlations between high on-task rates and teachers who used high levels of verbal behaviour including positive academic feedback. Teachers used three times more verbal approval for desired social behaviour in the classroom than has been reported in previous studies. It was found that teachers verbally interacted more with students during National Literacy and Numeracy Strategy lessons but that this did not lead to statistically significantly higher on-task rate. Similarly, teachers in inner-city schools interacted more with students, but on-task rates in inner-city schools were not significantly higher. Reasons for this effect are discussed. (Contains 8 tables and 11 figures.)