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The answer to that question appears to be a resounding yes.  According to The US Dept of Education publication, Reducing Class Size, What Do We Know? – March 1999, "the pattern of findings drawn from the existing research leads to the following Summary Research Conclusions:"

1. A consensus of research indicates that class size reduction in the early grades leads to higher student achievement. Researchers are more cautious about the question of the positive effects of class size reduction in 4th through 12th grades. The significant effects of class size reduction on student achievement appear when class size is reduced to a point somewhere between 15 and 20 students, and continue to increase as class size approaches the situation of a 1-to-1 tutorial.

2. The research data from the relevant studies indicate that if class size is reduced from substantially more than 20 students per class to below 20 students, the related increase in student achievement moves the average student from the 50^th percentile up to somewhere above the 60^th percentile. For disadvantaged and minority students the effects are somewhat larger.

3. Students, teachers, and parents all report positive effects from the impact of class size reductions on the quality of classroom activity.

Why Do Smaller Classes Make a Difference? (excerpts)

     The higher student achievement brought about by class size reduction may result from some of the ways in which reducing class size naturally alters the classroom environment. On being assigned to smaller classes, teachers report that the classroom atmosphere is better, that students can receive more individualized attention, and that the teachers have more flexibility to use different instructional approaches and assignments. One unanticipated result of the Burke County reduced class size initiative was that the teachers found themselves with more classroom space to work with, because they were using the same classrooms with smaller numbers of students. Class size reduction also changes the educational opportunities beyond the classroom, insofar as teachers have a larger portion of time to devote to working with each of their students’ parents.

     Class size reduction changes numerous features of the classroom situation. There are fewer students to distract each other. Each student in a reduced size class gets more attention on average from the teacher, and more time to speak while the others listen. Reduced class size also reduces the level of noise in a class. One theory offered to explain the positive effects of class size reduction on student achievement simply argues that in smaller classes each student receives a larger portion of the educational resources represented by the teacher's instructional time, and consequently, learns more.

      Other researchers have drawn attention to the quality of teaching in smaller classes, rather than the quantity. The SAGE evaluation study used teacher interviews, classroom observation, and other data-gathering techniques to study what happens in smaller classes, and these researchers suggest that students are benefiting from more individualized attention. The teachers know each of their students better, and can keep track of how each student is doing on the learning task of the moment. This knowledge enables the teacher to intervene more effectively to help the individual student make progress.

     Researchers also have suggested that smaller classes are more likely to be "friendlier" places, where students develop better relationships with their classmates and with the teacher, encouraging students to become more engaged in classroom learning activities. The smaller the class, the harder it is to escape the positive influence of the classroom educational experience. The explanation for why reduced class size is especially beneficial in the early grades may derive from the fact that in the early grades children are learning how to be students in classrooms where the number of people is larger than the number of people in their families and students are learning a new routine.  This socialization theory is also consistent with the research finding in both Project STAR and SAGE that the largest increase in student achievement occurs in the first year of a student's experience in a smaller class.

     The focus on class size reduction in the early grades also suggests that smaller classes represent a preventive, rather than a remedial, approach. If smaller classes help students start off on the right foot in learning how to adjust to the classroom situation and get engaged in learning activities, then students avoid the more difficult educational path of falling behind, finding help, and catching up to their schoolmates.

     The question of class size is not simply a matter of less is more. The pattern of research evidence only favors class size reduction if it is substantial and brings the class size below a certain threshold. Reducing class size from 30 to 25, for example, may well have no effect whatsoever. The research evidence from Project STAR showed that students in smaller classes with fewer than 18 students did better when compared with students in larger classes. Given the variations among individual students and teachers and the way they interact, it is unlikely that there is a single "magic number" below which class size suddenly produces a beneficial effect. But it is fairly clear that class size must get somewhere below 20 in order to make a real difference.

     Reducing class size to below 20 students leads to higher student achievement. However, class size reduction represents a considerable commitment of funds, and its implementation can have a sizable impact on the availability of qualified teachers. Strengthening teacher quality also leads to higher student achievement. There is more than one way to implement class size reduction, and more than one way to teach in a smaller class. Depending on how it is done, the benefits of class size reduction will be larger or smaller.

     Teachers do not necessarily change their behavior when they move to smaller classes. In one observational research study, even though the teachers assigned to smaller classes thought they were teaching differently, the independent observers saw no discernable difference in teacher behavior. Research studies suggest that teachers do not just automatically change their behavior to optimize the potential benefits of smaller class size, and there is a considerable body of research that shows that creating substantial changes in teachers' classroom behavior is no easy feat. Both teachers who are used to teaching in larger classes and teachers newly hired due to the hiring needs associated with class size reduction initiatives will need to have professional training and support to enable them to utilize more fully the advantages of smaller classes. It is clear that many schools will face this challenge in the coming years. The best⁸ ways to meet that challenge remain to be found.

Conclusion

     Reducing class size to below 20 students leads to higher student achievement. However, class size reduction represents a considerable commitment of funds, and its implementation can have a sizable impact on the availability of qualified teachers. Strengthening teacher quality also leads to higher student achievement. There is more than one way to implement class size reduction, and more than one way to teach in a smaller class. Depending on how it is done, the benefits of class size reduction will be larger or smaller.

The information above is provided from excerpts taken from the "The US Dept of Education's publication, Reducing Class Size, What Do We Know? – March 1999", To read this article in it's entirety, please click here.