It is still widely believed that the most important thing we can do for education is reduce class size. However, research over the past few years does not support this conjecture. Most recently, the Friedman Foundation reaffirmed what was already shown in research from the National Bureau of Economic Research in 2012 and prior to that in a paper released by ASCD. Class size in itself is not meaningful. Far more important is data-driven instruction.
“We find that traditionally collected input measures — class size, per pupil expenditure, the fraction of teachers with no certification, and the fraction of teachers with an advanced degree — are not correlated with school effectiveness,” write authors Will Dobbie and Roland G. Fryer Jr in their NBER paper. “In stark contrast, we show that an index of five policies suggested by over forty years of qualitative research — frequent teacher feedback, the use of data to guide instruction, high-dosage tutoring, increased instructional time, and high expectations — explains approximately 50 percent of the variation in school effectiveness”
http://www.washingtonpost.com/blogs/wonkblog/post/study-class-size-doesnt-matter/2012/01/28/gIQAaiZAYQ_blog.html
http://www.ascd.org/ASCD/pdf/journals/ed_lead/el_199004_robinson.pdf