Class Size and Academic Achievement

The consensus among many in education that smaller classes allow a better quality of teaching and learning has led to a policy of class size reductions (CSR) by a number of U.S. states, by the United Kingdom (UK) and Netherlands, and Asia Pacific countries as diverse as New Zealand and China. This policy is contentious, though: Some argue that the effects of CSR are modest and that there are other more cost-effective strategies for improving educational standards (Slavin, 1989; Rivkin, Hanushek, & Kain, 2000; Hattie, 2005).

Despite the important policy and practice implications of the topic, the research literature on the educational effects of class-size differences has not been clear. However, more recent research and reviews provide some answers, and this entry addresses whether class-size differences affect children's educational attainment and learning and classroom processes such as teaching and pupil behavior.

Class Size and Academic Achievement

Overall, much previous research has not had designs strong enough to draw reliable conclusions (Blatchford, Goldstein, & Mortimore, 1998). It has long been recognized, for example, that simple correlational designs, which examine associations between a measure of class size or pupil-teacher ratios, on the one hand, and measures of pupil attainment on the other are misleading because researchers often do not know whether the results can be explained by another factor, for example, that poorer performing pupils are placed in smaller classes. To arrive at more valid evidence two kinds of research design have been used.

Experimental Studies. The frequent assumption that the problems of correlational research are best overcome by the use of experimental research or randomized controlled trials, offers one reason for the great attention paid to the Tennessee STAR project. A cohort of pupils and teachers at kindergarten through third grade were assigned at random to three types of class within the same school: a small class (around 17 pupils), a regular (typical) class (around 23 students), and a regular class with a teacher-aide. In brief, the researchers found that in both reading and mathematics pupils in small classes performed significantly better than pupils in regular classes, and children from minority ethnic group backgrounds benefited most from small classes (Finn & Achilles, 1999; Nye, Hedges, & Konstantopoulos, 2000). In fourth grade the pupils returned to regular classes and the experiment ended, but gains were still evident after the following three years, that is, grades 4–6 (Word, Johnston, Bain, & Fulton, 1990).

Longitudinal Studies. There are some difficulties (e.g., concerning validity) with experimental studies (Goldstein & Blatchford, 1998), and an alternative approach is to set up longitudinal studies that measure the full range of class sizes and account statistically for other possibly confounding factors, including pupil differences at an earlier point. This approach was adopted in a large-scale UK study (Class Size and Pupil Adult Ratio, CSPAR) project (Blatchford, 2003; Blatchford, Bassett, Goldstein, & Martin, 2003; Blatchford, Moriarty, Edmonds, & Martin, 2002). This project tracked over 10,000 pupils in over 300 schools from school entry (at 4–5 years) to the end of the primary school stage (11 years). It used a multi-method approach and sophisticated multi-level regression statistical analyses.

The study found a clear effect of class size differences on children's academic attainment over the first year (4–5 years) in both literacy and mathematics. The effect size was comparable to that reported by the STAR project, and this trend is therefore supported by both experimental and non-experimental research designs. Small classes (fewer than 25) worked best in literacy for children with the lowest school entry scores who had most ground to make up. Effects of class size in the first year were still evident on literacy progress at the end of the second year of school, though by the end of the third year the effects were not clear. There were no clear longer-term effects of class size differences on mathematics achievement. Though this result indicates that the early benefits disappear after two years in school, there were no restrictions in terms of which size of class they moved to from year to year (in contrast with the STAR project).

The CSPAR's naturalistic design captured changes in class sizes from year to year. An important disruption effect on children's educational progress was found, that is, moving to a class of a different size, especially a larger class, had a negative effect on progress.

Possible Effects of Class Size on Teachers and Pupils

Despite the widely held view that small classes will lead to a better quality of teaching and learning, the research evidence has not been clear. One reason is the often-anecdotal nature of much research. Finn, Pannozzo, and Achiles (2003) point out the need for systematic, preferably observational, research in this field. Overall, reviews of research suggest that class size effects are likely to be not singular but multiple, and that it is difficult in one study to capture all the complexities involved.

Effects on Teachers. Perhaps the most consistent finding is that class size affects individualization of teaching. The smaller the class, the greater the likelihood is that a teacher will spend more time with individual pupils. In smaller classes there also tends to be more teaching overall. Large classes present more challenges for classroom management, pupil control, and marking, planning, and assessment. Teachers are put under more strain when faced with large classes. Qualitative studies suggest that in smaller classes it can be easier for teachers to spot problems and give feedback, identify specific needs and gear teaching to meet them, and set individual targets for pupils. Teachers also experience better relationships with, and have more knowledge of, individual pupils.

Effects on Pupils. Finn, Pannozzo, and Achiles (2003) conclude that students in small classes in the elementary grades are more engaged in learning behaviors, and they display less disruptive behavior than do students in larger classes. The CSPAR study found in the case of four to five year old pupils more disengagement in large classes but no effects in 10 to 11 year old pupils, possibly because of assessment and curriculum pressures at that age. In large classes pupils were more likely to simply listen to the teacher while in smaller classes pupils interacted in an active way with teachers, by initiating, responding, and sustaining contact (Blatchford, Bassett, & Brown, 2005).

Curriculum Effects. Research shows a moderating role of school subject on relationships between class size and classroom processes. Rice (1999) found that in mathematics, but not science, as class size increased, less time was spent on small groups and individuals, innovative instructional practices, and whole group discussions. In the CSPAR study, the overall effects of class size on individualized attention were found in all subjects but English. One direction for future research is to identify more precisely ways in which class size effects vary in relation to particular school subjects and student age.

Implications for Policy and Practice

Overall, results suggest that while small classes will not make a bad teacher a good one, they can allow teachers to be more effective; conversely, large classes inevitably present all teachers with difficulties and the need for compromises. Small classes can offer opportunities for teachers to teach better (Anderson, 2000) or, to use a different term, they can create facilitating conditions for teachers to teach and students to learn (Wang & Finn, 2000).

Age of Pupil. Research shows that the age of the child needs to be taken into account when class size effects are considered. There is a clear case for small class sizes in the first years of school. Results show where resources could be further targeted, that is, classes smaller than about 20 to 25 for those with most ground to make up in literacy skills. Another policy implication is to maintain smaller classes across years where possible.

Age versus Start Up Effect. Research also suggests that class-size reduction initiatives are best seen as a policy of prevention but not remediation, in the sense that the evidence supports the use of small classes immediately after entry to school, but there is little evidence that small classes introduced later in children's school lives are as effective. However, there is still the possibility that smaller classes may be advantageous at later strategic points of transition in students' school lives, for example, in the first year of secondary education. Research evidence on this possibility is needed.

Implications for Practice. It has often been pointed out that teachers do not necessarily change the way they teach when faced with smaller classes, and this fact might well account for the relatively modest effects of class size on achievement. Blatchford, Russell, Bassett, Brown, and Martin (2007) have suggested several ways in which CSR can be accompanied by pedagogical changes to enhance beneficial effects for students, for example, taking advantage of the possibilities of increased individualization; adopting more adventurous and flexible teaching; and implementing more effective collaborative learning between pupils. Some have argued that teacher professional development is a better investment than CSR, but it is preferable not to see them in opposition. Rather, professional development should be used to help teachers see pedagogical opportunities in small classes and develop strategies for realizing educational objectives in small (and large) classes.


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