classroom learning

Class Size: Does it Matter?

  • Research into class size has been mixed partly because few studies have directly manipulated class size and successfully removed any other factors that could influence learning, and partly because of there has been no consistency in what constitutes a "small" or "reduced" class size.
  • Evidence points to a class size of 15 students or less being necessary to show clear benefits.
  • Small class size is more important in the early years.
  • Small class size may have greater benefit for disadvantaged students.

While parents and teachers have always strongly supported small class sizes, their belief has not always been supported by evidence. Part of the problem lies in that word “small” — what constitutes a small class? Different interventions have looked at reducing class sizes from 40 to 30, or 30 to 25. It may well be that such reductions are not sufficient to show clear benefits.

The STAR Project

The project everyone talks about, the STAR project (Student Teacher Achievement Ratio), looked at class sizes well below these. The longitudinal study was undertaken in the American state of Tennessee and involved over 7000 students from 79 schools. For three years, from kindergarten through grade 3, students were placed either in small classes of 13-17 students; regular classes of 22-25 students; or regular classes with a teacher aide. Those in smaller classes performed significantly better on tests than those placed in regular classes. The largest gains occurred in inner-city schools.

Excitingly, the advantage was not only maintained in subsequent years but actually increased: in grade 4, students who had been in smaller classes were 6-9 months ahead of regular class students in reading, math, and science; by grade 8, they were a year ahead. Later, almost 44% of small class size students took college entrance exams, compared to 40% of regular class size students — the difference was greatest for African-Americans; 40.2% compared to 31.7%. 72% of small class students graduated from high school on schedule, compared to 65-6% of regular class students. They were also more likely to complete high school, to graduate with honors, to complete advanced math and English classes.

The SAGE Project

More recently, in Wisconsin, the Student Achievement Guarantee in Education (SAGE) program has reduced the student-teacher ratioto 15:1 in K-3 classrooms in 30 schools, comparing their performance to 14-17 matched schools. The benefits seen were again particularly great for African-American students, who reduced the achievement gap with white students by 19% — in comparison schools, the achievement gap widened by 58%. Interestingly, the results of having 2 teachers in a class of 30 were the same as having 2 classes of 15.

Why have different studies found different results?

Let’s look a little further at why there has been confusion about what educational research has told us about class size, given that this is one of the most studied issues in education. Howard Blake in 1954 reviewed pre-1950 studies. He found 85 that were based on original research, and of these 35 found benefits of small classes, 18 found benefits to large classes, and 32 found no difference. But Blake analyzed the studies further, looking for scientific acceptability. He found only 22 studies that reached this standard (a not surprising result for educational research in this time period). Of the 22, 16 favored small classes, 3 favored large classes, and 3 were inconclusive.

A meta-analysis of 77 studies in 1978 (Glass, Cohen & Smith) concluded that the greatest benefits occurred when class sizes were reduced to 15 students or less. A follow-up study suggested that the benefits were greatest for those below the age of 12 (Smith et al, 1979).

Unfortunately, educational experiments such as STAR — where students are randomly assigned to different treatments — are rare. More usual are attempts at indirectly investigating class size by comparing different situations. This, obviously, has many problems. You can get a feeling for these by reading a British analysis at: Apart from anything else, it shows you how one type of statistical analysis in studies of this nature can come up with no clear benefits of class size, while another type shows a very clear benefit.

It also seems that the principal benefit of reduced class size lies in its effect on the teacher; clearly some teachers will be more affected by this than others.

It is also worth noting the considerable international variation in class size -- a variation showing no correlation with performance -- indicating that class size cannot be considered out of the context of teaching method. The TIMSS international study, for example, found that although the average eighth-grade mathematics class was 31 students, there was considerable variation even among the higher-performing countries –- from 42 students in Korea to 19 in Belgium.


Many policy-makers argue that, while class size may be of value, the benefit doesn’t warrant the huge amount it would cost, given that there are other ways to spend the money — more and better trained teachers, for example. And, certainly, there would seem little benefit to reducing class size if you can’t put qualified teachers in the classes. Class size isn’t a factor that can be considered in a vacuum. But it does seem clear that:

  • class size can be an important factor in learning outcomes,
  • it is more important in the early years,
  • it is more important for disadvantaged students,
  • benefits may not be seen unless the class size is reduced to around 15.


For more about the results from Project STAR, see

The National Education Association (U.S.) has information about class size at:

TIMSS has an interesting international comparison of class size and math achievement at:

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Homework: is it worth it?

  • Overall, homework does appear to result in higher levels of achievement for older students (at the secondary level).
  • For these students, more time spent on homework is associated with higher levels of achievement, although there is probably a level beyond which more is counterproductive (perhaps at three hours a day).
  • For students aged 11-13, homework appears to be of benefit, but not to the same degree as for older students.
  • For these students, spending more than an hour or two on homework does not result in greater benefit.
  • There is little evidence of benefit for students younger than 11, although it can be plausibly argued that small amounts of homework can have an indirect benefit for promoting good study habits and attitudes to learning.

The Suggested Benefits of Homework

The most obvious presumed benefit of homework is, of course, that it will improve students' understanding and retention of the material covered. However, partly because this (most measurable) benefit has not been consistently demonstrated, it has also been assumed that homework has less direct benefits:

  • improving study skills, especially time management
  • teaching students that learning can take place outside the classroom
  • involving parents
  • promoting responsibility and self-discipline

The Possible Negative Effects of Homework

Probably the most obvious negative effect is the stress homework can produce in both student and parent. Homework can be a major battleground between parent and child, and in such cases, it's hard to argue that it's worth it. There are other potential problems with homework:

  • homework demands can limit the time available to spend on other beneficial activities, such as sport and community involvement
  • too much homework can lead to students losing interest in the subject, or even in learning
  • parents can confuse students by using teaching methods different from those of their teachers
  • homework can widen social inequalities
  • homework may encourage cheating

What Research Tells Us

Because homework has been a difficult variable to study directly, uncontaminated by other variables, research has produced mixed and inconclusive results. However, it does seem that the weight of the evidence is in favor of homework. According to Cooper's much-cited review of homework studies, there have been 20 studies since 1962 that compared the achievement of students who receive homework with students given no homework. Of these, 14 showed a benefit from doing homework, and six didn't.

The clearest point is the striking influence of age. There seems, from these studies, to be a clear and significant benefit to doing homework for high school students. Students 11 to 13 years of age also showed a clear benefit, but it was much smaller. Students below this age showed no benefit.

In 50 studies, time students reported spending on homework was correlated with their achievement. 43 of the 50 studies showed that students who did more homework achieved more; only 7 studies showed the opposite. The effect was greatest for the high school students and, again, didn't really exist for the elementary school students.For the students in the middle age range (11-13 years), more time spent on homework was associated with higher levels of achievement only up to one to two hours; more than this didn't lead to any more improvement.

TIMSS, however, found little correlation between amount of homework and levels of achievement in mathematics. While they did find that, on average, students who reported spending less than an hour a day on homework had lower average science achievement than classmates who reported more out-of-school study time, spending a lot of time studying was not necessarily associated with higher achievement. Students who reported spending between one and three hours a day on out-of-school study had average achievement that was as high as or higher than that of students who reported doing more than three hours a day.

Two British studies found that while homework in secondary schools produced better exam results, the influence was relatively small. Students who spent seven hours a week or more on a subject achieved about a third of an A level grade better than students of the same gender and ability who spent less than two hours a week.

How much homework is 'right'?

A survey conducted by the United States Bureau of the Census (1984) found that public elementary school students reported spending an average of 4.9 hours and private school elementary students 5.5 hours a week on homework. Public high school students reported doing 6.5 hours and private school students 14.2 hours. Recent research studies by the Brown Center on Education Policy concluded that the majority of U.S. students (83% of nine-year-olds; 66% of thirteen-year-olds; 65% of seventeen-year-olds) spend less than an hour a day on homework, and this has held true for most of the past 50 years. In the last 20 years, homework has increased only in the lower grade levels, where it least matters (and indeed, may be counterproductive).

In America, NEA and the National PTA recommendations are in line with those suggested by Harris Cooper: 10 to 20 minutes per night in the first grade, and an additional 10 minutes per grade level thereafter (giving 2 hours for 12th grade).

In Britain, the Government has laid down guidelines, recommending that children as young as five should do up to an hour a week of homework on reading, spelling and numbers, rising to 1.5 hours per week for 8-9 year olds, and 30 minutes a day for 10-11 year olds. The primary motivation for the Government policy on this seems to be a hope that this will reduce the time children spend watching TV, and, presumably, instill good study habits.

TIMSS found that students on average across all the TIMSS 1999 countries spent one hour per day doing science homework, and 2.8 hours a day on all homework (the United States was below this level). On average across all countries, 36% of students reported spending one hour or more per day doing science homework.

There is some evidence that the relationship between time on homework and academic achievement may be curvilinear: pupils doing either very little or a great deal of homework tend to perform less well at school than those doing 'moderate' amounts. Presumably the association between lots of homework and poorer performance occurs because hard work is not the only factor to consider in performance -- ability and strategic skills count for a great deal, and it is likely that many very hard-working students work so long because they lack the skills to work more effectively.

What makes homework effective?

By which I mean, what factors distinguish "good", i.e. useful, homework, from less productive (and even counterproductive) homework. This is the $64,000 question, and, unfortunately, research can tell us very little about it.

Cooper did conclude that there is considerable evidence that homework results in better achievement if material is distributed across several assignments rather than concentrated only on material covered in class that day.

There is no evidence that parental involvement helps, although it may well be that parental involvement can help, if done appropriately. Unfortunately, parental involvement can often be inappropriate.

Can students really watch TV or listen to music while doing homework?

A burning question for many parents!

A British study found that watching TV while doing homework was associated with poorer quality of work and more time spent. However, simply listening to the soundtrack did not affect the quality of the work or time spent. It's assumed that it's the constant task-switching caused by looking back and forth between the screen and the work that causes the negative effect. From this, it would also seem that listening to the radio should not be a problem. It's worth noting that we become less able to multi-task as we age, and that parents' objections to their children's study environment probably reflect their awareness that they themselves would find it difficult to concentrate in such circumstances.


You can read the TIMSS report at:

You can read an article on the motivational benefits of homework at:

And there are more articles about homework, with more details of Cooper's review at:

And a British review of homework research is available at:


April 2012: my update to this article.

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Desirable difficulty for effective learning

When we are presented with new information, we try and connect it to information we already hold. This is automatic. Sometimes the information fits in easily; other times the fit is more difficult — perhaps because some of our old information is wrong, or perhaps because we lack some of the knowledge we need to fit them together.


D’Mello, S., Lehman B., Pekrun R., & Graesser A. (Submitted). Confusion can be beneficial for learning. Learning and Instruction.

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The changing nature of literacy. Part 2: Lecturing

This post is the second part in a four-part series on how education delivery is changing, and the set of literacies required in today’s world. Part 1 looked at the changing world of textbooks. This post looks at the oral equivalent of textbooks: direct instruction or lecturing.

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Maybe it has nothing to do with self-control

I recently reported about a finding that refines a widely-reported association between self-regulation and academic achievement. This association relates to the famous ‘marshmallow test’, in which young children were left alone with a marshmallow, having been told that if they could hold off eating it until the researcher returns, they would get two marshmallows.


McGuire, J. T., & Kable, J. W. (2013). Rational Temporal Predictions Can Underlie Apparent Failures to Delay Gratification. Psychological Review, 120(2), 395–410. doi:10.1037/a0031910

Baumeister, R. F., & Scher, S. J. (1988). Self-defeating behavior patterns among normal individuals: Review and analysis of common self-destructive tendencies. Psychological Bulletin, 104, 3–22. doi:10.1037/ 0033-2909.104.1.3

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Should learning facts by rote be central to education?

Michael Gove is reported as saying that ‘Learning facts by rote should be a central part of the school experience’, a philosophy which apparently underpins his shakeup of school exams. Arguing that "memorisation is a necessary precondition of understanding", he believes that exams that require students to memorize quantities of material ‘promote motivation, solidify knowledge, and guarantee standards’.

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