"Time is the most valuable thing a man can spend" – Theophrastus

If time is the most valuable thing a man can spend, does the amount of time spent in the classroom have any bearing on academic success? The question is an important one, as policy-makers and those working in ministries of education often set guidelines on recommended taught time. School boards, school heads and ultimately teachers make decisions on how much time should be spent teaching different subjects in schools – and often the subjects considered  more "important" end up with more teaching time devoted to them. However, should we really assume that the more we teach a subject in school, the better students will perform?

Common sense tells us that there must be a relationship between time and achievement. Research results also back this up. Mozart must have devoted a lot of time to playing music as a child, while Lionel Messi must surely have spent his childhood doing little more than kicking a football. But while we all acknowledge a relationship between time and performance, it's also clear that not all children spending plenty of time on music or football end up as Mozart or Messi. So what about academic subjects within school curriculum such as mathematics? Will intended teaching time make a big difference to overall achievement?

To explore this further, we can compare information on Recommended annual taught time in full-time compulsory education by Eurydice with international test results such as PISA Programme for International Student Assessment (PISA) results from 2012. The PISA exams are taken by 15 year olds students, one year before the end of compulsory education in most countries. Where recommendations exist, the average number of recommended teaching hours intended to be received by students up to the age of 15 years old in Europe in mathematics is around 1072 hours. In terms of PISA results, the best performing European countries include Liechtenstein, Estonia and Finland.

While Liechtenstein has many more recommended hours than the European average (between 1285 and 1314 depending on the type of school), Estonia (944 hours) and Finland (912 hours) have considerably less. It is also worth noting that there are many examples of education systems with a much higher number of recommended instruction hours for mathematics where PISA results are rather average, such as France (1584 hours) and Luxembourg (1412 hours). There are also countries that performed very well in PISA 2012, such as Belgium and the Netherlands, where recommended instruction time plays little or no role, and schools have the autonomy to decide how much time is devoted to subjects. So there appears to be only a weak correlation between recommended instruction time and strong PISA results.

What about countries that perform less well in maths? Perhaps the curriculum does not devote enough time to the subject? The lowest scoring European countries in mathematics in PISA 2012 are Cyprus and Bulgaria where there are 937 and 759 recommended hours respectively. At first glance, it appears that these countries are indeed spending relatively little time on the subject as these recommended hours are both considerably below the European average. However, before getting carried away by this discovery, we should also note that other countries with a relatively low number of recommended hours such as Slovenia (988 hours) and the Czech Republic (999 hours) did relatively well in PISA tests – 10th and 12th among European countries. So even if teaching time may be part of the problem for low performing countries, it's certainly not the only issue.

So what other factors are at play when looking at students' opportunity to learn? Firstly, we need to remember that time spent in the classroom tells us nothing about the quality of teaching and learning that is taking place. The OECD has concluded in an analysis of the impact of after-school lessons that it is the quality of lessons rather than the quantity of hours that has the most impact on student performance. Eurydice's 2012 study on mathematics education in Europe also pointed to effective and varied teaching methods as a prime means to improve learning.

We should also bear in mind that the perception of the importance of a subject could be a factor. The share of hours dedicated to subjects may send a message that some lessons are more or less important than others, thereby requiring students to study more or less in their own time – and also lessening our ability to draw a conclusion about the link between taught time and PISA results. In addition, in some countries, especially in the upper grades of compulsory education, students have the choice to take options, one of which may be additional lessons in mathematics. Moreover the hours quoted in Recommended annual taught time in full-time compulsory education in Europe, 2011/12 are just that – recommended – and almost certainly not the actual number of teaching hours that take place.

In the end, the key challenge is to provide quality opportunities for students to engage in mathematics in a way that they find stimulating. As for the relationship between recommended time and student performance, we should be careful in interpreting statistics, recognising the error of focusing on one issue when many factors are at play. As the famous quote attributed to Disraeli reminds us, "there are three kinds of lies: lies, damn lies, and statistics".

Authors: Orla Colclough and David Crosier