Does class size affect student achievement.  For decades, this debate has been shaped by the studies conducted to measure achievement.

Math and first (native) language test scores showed a negligible effect.  As these were the only measures, the data remained static for years.

However, Dr. Peter Blatchford from University College London, and colleagues have done extensive research into other factors that can influence achievement other than math and language arts.

His team found there are many more factors to consider, such as student attainment differences in a class, classroom structure and basic pedagogy.

Universal Design for Learning is an evidence based instructional framework that works well in general education settings.  However, based on teacher feedback and on the ground experience, class sizes matter a great deal.  30 students is a very difficult number to implement effective education reforms.

Research is inconsistent due to issues like those mentioned here, but numbers for lower elementary school should ideally be no more than 15, in the hosts (not paying attention to research but to experience, probably a bad idea) opinion.  

References:

Peter Blatchford blog link:

https://www.bera.ac.uk/blog/rethinking-class-size-the-complex-story-of-impact-on-teaching-and-learning

Summary

The podcast discusses how increasing class sizes and the elimination of special day classes negatively affect inclusion for students with disabilities. The host shares personal observations about specific deficits (attention, processing, sensory, social, learning) that are exacerbated in larger classes. Research by Dr. Peter Blatchford is cited to argue that the impact of class size is complex, affecting classroom processes, teacher well-being, and broader pupil outcomes beyond just academic scores.

Key takeaway

Impact of Large Class Sizes on Students with Disabilities

Larger classes create chronic difficulties for students with disabilities, leading to gaps in learning and social skills.

The host notes from personal experience that attention and focus deficits, slow language processing, sensory overload, social skills deficits, and learning disabilities (especially in reading/writing) are common and can result in emotional dysregulation and classroom disruptions.

Eliminating mild to moderate special day classes and placing students in general education to save money worsens inclusion outcomes.

The host mentions that some districts are adopting this practice, which has negative effects that are not reflected in aggregate math and language arts scores.

Universal Design for Learning Implementation Challenges

Large class sizes put tremendous pressure on teachers to fully or partially implement Universal Design for Learning (UDL).

The host explains that UDL – teaching to strengths, gaining student buy-in, and assessing through preferred modalities – is proven effective but becomes difficult to execute when student numbers are high.

Research on Class Size: Beyond Academic Attainment

Exclusive focus on class size–attainment correlations is misleading; the real impact is on classroom processes.

Dr. Blatchford's research shows that class size is interconnected with teacher management, group work, peer relationships, task nature, and administrative activities; large classes create profound problems especially when student attainment levels are diverse.

Large classes negatively affect teachers’ well-being and retention.

The host cites research that teachers absorb negative consequences through more demanding management, extra individual support, and excessive marking in their own time.

Class size affects broader pupil outcomes such as on-task behavior, creative work, investigative skills, and independent working.

Children in larger classes, especially low-attaining students, show more off-task behavior; the effects on pupil development go beyond standardized test scores.

Thanks to Soundimage.org for the free access to the AI generated music used in this podcast (https://soundimage.org/)