Students cramming for their exams may indeed be reducing their long-term retention, according to a study published in the journal, Current Directions in Psychological Science.

The study suggests that  'massing' all the study on a single topic into a single session reduces long-term retention, and that it is always better to leave it alone for a while and then return to it.

University of South Florida [Images] psychologist Doug Rohrer and Hal Pashler of the University of California, San Diego, made two groups of students study new vocabulary in different ways.

The researchers wanted to determine whether 'over-learning', the term learning specialists use for studying material immediately after a person has mastered it, was a waste of valuable time or did that extra effort embed the new memory for the long haul.

They found that one group of students ran through the list five times, and participants therein got a perfect score no more than once. The other group kept drilling for a total of 10 trials, and with that extra effort, the students had at least three perfect run-throughs.

The psychologists then tested some students one-week later, and others four weeks later. Among students who took the test a week later, and who had done the extra drilling performed better. However, the benefit of over-learning completely disappeared by four weeks.

The finding indicates that students who are interested in learning that lasts for a longer period, cramming is really a waste. They should instead spend this time looking at material from last week or last month or even last year.

Rohrer and Pashler also wanted to see if the duration of study breaks might make a difference in learning, and they found that it actually did. When two study sessions were separated by breaks ranging from five minutes to six months, with a final test given six months later, students did much better if their break lasted at least a month.

So, rather than distribute their study of some material across just a few days, as millions of schoolchildren do when given a different list of vocabulary or spelling words each week, students would be better off seeing the same words throughout the school year.

Rohrer and Pashler also found similar effects with more abstract learning, like maths. They say that since most mathematics textbooks now are organised to encourage both over-learning and massing, students end up working 20 problems on the same concept when they should be working 20 problems drawn from different lessons learned since the beginning of the school year.

Researchers believe that due to all this, students are wasting a lot of precious learning time.