The effect of class size on educational achievement

KindergartenDespite evidence that children in smaller primary classes in the United States do better academically, there is still debate in England about the effects of class size. Researchers Peter Blatchford, Paul Bassett, Harvey Goldstein and Claire Martin, Institute of Education, University of London, summarized results from the most complete analysis of the educational consequences of class-size differences in the United Kingdom. The study had two goals: first, to establish whether class size affects students’ academic achievement; and second, to study connections between class size and classroom processes, which might explain any differences in achievement. Like research in the U.S., this study showed that there was a clear effect of class size difference on children’s academic achievement in the first year. Children with the lowest scores on school entry benefited the most from small classes.

This study was designed to improve on previous research. It used an observational approach to capture the nature of the relationship between class size and achievement across a range of class sizes and a longitudinal design with baseline assessment to follow children for several years. The sample included over 10,000 5-to-7-year-old children who were monitored from school entry through the primary grades. Rigorous statistical procedures were followed to control for factors that might affect the relationship between class size and academic achievement.

Multiple effects were found. In smaller classes, teachers had more contact with individual students and students had more support for learning. In large classes there were more and larger groups, which posed instructional and management difficulties for teachers. Students in large classes were more often inattentive or off-task. These results support a contextual approach to classroom learning within which class size differences have effects on both teachers and students. Much depends on how teachers adapt their teaching to different class sizes, these researchers report. They believe that teacher training and professional development can do more to address contextual features like class size.

Conditions in English Primary Classrooms

Class sizes vary greatly in England. Primary classes range from under 20 to over 35 children. Educators need to know whether a class of 30 with two adults is equivalent to two small classes of 15, and whether the addition of a teaching aide benefits student achievement. Given the huge financial implications of reducing class sizes and hiring more staff, there is a lot at stake in class-size research.

Because previous research in the United States has shown that the strongest effect of class size differences is on the youngest children in school, this study was designed to measure the effects of existing class sizes on children’s first three years in school. In addition to academic achievement, five main areas of classroom processes were studied:

  1. Within-class groupings (size and number of groups)
  2. The amount of individual teaching, procedural, social and disciplinary interactions
  3. Individual support for reading
  4. Pupil inattentiveness
  5. Peer relations

Both qualitative and quantitative methods were used to gather data on these processes. Detailed case studies were carried out to describe teaching methods, the contribution of teaching assistants and teachers’ and students’ experiences in different class sizes. Two groups entering school one year apart were followed for three years. All children entering randomly selected schools were included in the study. The schools in the study drew from a wide range of social backgrounds and from urban, suburban and rural areas. All children were tested on literacy and mathematics upon entering school and at the end of each of their first three years.

Class Size Study Results

Classroom process proved to be connected to class size differences. Primary school students in England spend a lot of time working in groups within their classroom. The predominant group size was four to six students but larger groups of 11 or more students were common in large classes. Consistent relationships were found between class size and time spent teaching; the smaller the class, the more teaching. There was also a correlation between class size and non-teaching time: The larger the class, the more time was spent on non-teaching activities. Children in smaller classes interacted with their teachers more often than those in larger classes. In large classes, children read to their teachers less often and for less time than in small classes. Children in small classes were also more likely to be the focus of their teacher’s attention on a one-to-one basis. Effective teaching may be possible in large classes, but at some cost to the teachers who work longer hours with fewer breaks, eventually reducing enthusiasm and job satisfaction.
Significant effects on students were related to class size. In smaller classes, students not only had more active involvement with their teacher; they had more active roles themselves. Students in large classes were twice as likely to be off task as students in smaller classes. Social relations between students were not strongly related to class size. Students in large classes spent more time with each other, but peer relations were as good as or better than in small classes.

The effect of class size on literacy and math achievement was studied for each of three years separately. At the beginning of the study, students were identified as in the top 25 percent, middle 50 percent or lowest 25 percent academically. There was a statistically significant increase in achievement for all three groups, although the effect was greatest for those beginning in the lowest achievement level. For literacy achievement, a reduction in class size from 30 to 20 pupils in the first year of school resulted in an increase of one-third of a standard deviation for the low group and about half that size increase for the middle and top groups. In contrast, for first-year mathematics, the effect of class size was statistically significant (.25 SD) and equal for all three groups of children. Class size did not have a significant effect on achievement in either reading or math in the second and third years of school. However, gains made in small classes in the first year were only sustained the following year if the student was kept in a small class. Moving to a larger class after one year appeared to cause the child to lose the progress made in the first year. Although teachers were generally positive about the contribution of teaching assistants, there was no evidence that additional staff or adults in the class increased achievement.

Clear case for small classes in first year

In this study researchers found that class size is related to several classroom processes, producing multiple effects. Statistical analysis used in this study narrowed down the likely processes connected to both class size and achievement and helped identify variables to be examined in future studies. The effect of class size in the first year of school is impressive, even after adjusting for other variables. Results are comparable to those of the STAR project in Tennessee. These results show that it is important to take into account the age of the child when considering class-size effects. There is a clear case for reducing class sizes in the first year of school. There is no evidence that small classes introduced later in children’s school lives are as effective. Small classes appear to increase literacy progress for the children who enter school with the fewest skills. No clear longer-term effects of small classes on literacy achievement was apparent in this study. Moving to a larger class, however, was disruptive to the progress students made in their first year. It is advisable to maintain smaller classes in the second year.

Researchers caution that there were limitations to this study. The study was not designed to determine an optimal class size, but the biggest gains for the least skilled students were achieved in classes with fewer than 25 students. Researchers are continuing to study these students as they progress through school to determine the long-term effects of small classes in the early years. They also point out that there may be other outcomes related to class size that were not measured.

“Are Class Size Differences Related to Pupils’ Educational Progress and Classroom Processes? Findings from the Institute of Education Class Size Study of Children Aged 5-7 Years”, British Educational Research Journal, Volume 29, Number 5, October 2003, pp 709-730.

Published in ERN February 2004 Volume 17 Number 2

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