Many factors affect a high school student’s ability to excel in science classes. Smaller classroom sizes are generally thought to improve most subjects’ lessons, especially reading and mathematics, but few studies have been conducted that look at science achievement. 

Dr. Ting Shen, assistant professor of psychological science at Missouri S&T, is conducting an analysis of the Program for International Student Assessment (PISA) 2015 data from 26 countries, including 24 European countries plus the U.S. and Canada, to see the full impact of small-class sizes on science achievement in secondary education.

Her work, which aims to explore how class size affects student outcomes in science disciplines, provides insights for future educational policy and teaching practices. Shen’s findings are reported in the journal Studies in Educational Evaluation.

“Class size policies are highly debated because it is often a variable that is manipulated to control spending on education at the state level,” says Shen. “Small classes are supported by parents and teachers, while policymakers and academics occasionally have different opinions regarding its importance related to learning.”  

In Shen’s study, small class is defined as 20 or fewer students in a classroom and this threshold is regarded as the standard recommended cutoff point for American small classes. 

Shen’s research tried to reduce various environmental factors and estimation bias by controlling systematic differences between students in small and large classes using advanced statistical methods (i.e., propensity score analysis and meta-analysis). The project had to consider things such as student demographics variables, socio-emotional variables, classroom science learning environments, and even overall school variables, while also looking at schools from different countries.  

“Science knowledge is more likely to be taught to students in a classroom, so learning environment matters as students’ science learning occurs during their interactions with peers and teachers in classes of different sizes,” says Shen. “We have to consider specific aspects of science learning environments too, such as teacher support, teacher-directed science instruction, science learning time, and the amount of science activities used in a lesson.” 

The results of her research found that the effects of small classes on science achievement were statistically significant and negative in nine countries, while in 17 other countries small-class effects were not significant. Shen also used meta-analysis to combine effect sizes, and her findings show that the effects of small classes were significant and negative, suggesting that students in medium or large classes had higher science achievement, but the overall effect size was small. 

In general, countries’ class size policy of maximum sizes was not related with the findings. For example, Austria, Czech Republic, Germany, Greece, Hungary, Italy and Slovenia had maximum class size rules and had significant estimates of small classes, while Bulgaria, Lithuania, Luxembourg, Portugal, Slovenia and Spain also had maximum class size rules, but the results were not significant. Shen says that two reasons for this are possible: first, these rules may change frequently from year to year over time in each country; second, these rules may not be followed in some countries. 

“There is no clear pattern of whether or when class size may affect 15-year-old students’ science achievement,” says Shen. “However, it is consistent with the conclusion that class size effects are more country and context specific in previous studies of class size.”  

About Missouri S&T  

Missouri University of Science and Technology (Missouri S&T) is a STEM-focused research university of over 7,000 students located in Rolla, Missouri. Part of the four-campus University of Missouri System, Missouri S&T offers over 100 degrees in 40 areas of study and is among the nation’s top public universities for salary impact, according to the Wall Street Journal. For more information about Missouri S&T, visit  www.mst.edu.