It seems every Tom, Dick and Sally has something to say about education, and very seldom do they agree on anything. Even where the various parties do agree at a broad level, such as the quality of teachers being important, there is still huge divergence in the views when it comes to the detail.

Recent PISA results show that although New Zealand’s overall education quality is high, the greatest variance in achievement is found within schools rather than between schools. This implies that differences are likely to be found behind closed doors of classrooms. The divide in the sector about how, or even if teacher quality should be measured, is massive. 

After all, should teachers be held accountable for students’ backgrounds, abilities, parents’ educational background and so on? What possible good can there be in pitting teachers against each other when you cannot control for the differences in students? Without taking these factors into consideration, the validity and reliability of using NCEA or National Standards results to find out who is a good or bad teacher is highly questionable.

It is clear then why the issue is contentious.

Luckily, recent research coming out of the US suggests this might be an area of the education debate where differences can be resolved. The 2013 study looked at teacher value-added (VA) as a measure of quality, but managed to control for student differences such as parental background and individual ability, as well as sorting bias. Their data-set was notable too, covering more than 20 years of test scores for over 2.5 million pupils.

They found no evidence of bias in VA estimates using previously unobserved characteristics.  

They went further. Using income-tax data, they were also able to link students assigned with high-VA teachers with better life outcomes. On average, a one standard deviation improvement in teacher value-added in a single grade raises earnings by about 1% at age 28. The researchers also found that good teachers lower the chance of teenage pregnancy.

This method seems fairer than simply comparing student achievement scores without considering compounding factors. VA measures are all about showcasing growth due to teacher input, while taking individual student characteristics into consideration.

Employing value-added measures in New Zealand schools would not only allow effective practice to be identified and shared, but also to help teachers be more effective at equipping young minds with a great education.