In the 1960s, research by Endel Tulving demonstrated that, as with studying, being tested on material is not a neutral process but rather a beneficial process that helps individuals retain the information. Known as the “testing effect,” this idea dates as far back as 1917 to work by Arthur Gates.

Since then, many researchers have demonstrated that replacing additional studying sessions with testing sessions improves long-term retention of information. In research conducted by Robert Hogan and Walter Kintsch (1971), participants studied a list of words four times (SSSS) or studied it once and recalled it three times (STTT). Despite the STTT group only re-experiencing the words that they could recall as opposed to studying the full list of words repeatedly, the test group had better long-term retention of the words.

In 2007, Jeffrey Karpicke and Henry Roediger from Washington University in St. Louis published a study in the Journal of Memory and Language which supported the main conclusion of previous studies, namely, that “repeated retrieval of information is key to long-term retention,” and examined which conditions could best benefit long-term retention.

Previous research has shown that repeated study is beneficial over repeated testing when the recall happens immediately, but that repeated testing is beneficial in situations where the test comes anywhere from two days to a week later. What this means in practical terms is that if you’re cramming the same day of your exam, you’re better off just repeatedly reading over the material. However, if you’re studying a few days or weeks in advance, testing yourself on what you’ve studied will help you more come exam time.

In the 2007 experiment, 60 participants were divided evenly into three conditions: a standard condition (STST), a repeated study condition (SSST), and a repeated test condition (STTT). In the study phase — which consisted of cycling through a list of 40 words five times — they were instructed to study the words for later recall.

Both the predictions and results of Karpicke and Roediger’s study were in line with the wisdom from previous studies. Despite participants only studying the list five times in the one study session condition (STTT), recall performance one week later was seven per cent better than recall from participants who studied the list 15 times in three study sessions in the SSST condition. Recall performance in the standard condition (STST) was even better with a total of 68 per cent of the words recalled, an increase of four per cent over STTT.

According to these results, alternating between study and test phases is the best way to prepare for an upcoming exam. The researchers hypothesize that the advantage lies in the more frequent feedback that occurs in the STST scenario than in SSST or STTT. This means that after a test trial, when studying the words again, the words that are recognized by the participant as not being recalled will be more distinct and remembered better, and will subsequently be recalled early on in the next testing phase.

A second experiment in the study by Karpicke and Roediger demonstrated again that repeated testing is the key to remembering information later, this time by looking at the studying and testing of words that had already been reviewed in a testing phase. When words that had already been reviewed in a practice test were studied again, it did little to aid in remembering. However, by testing words that had already been reviewed, test performance one week later was significantly better. This result suggests that over-learning — practicing material that is already known well enough to be recalled during an exam — can be a good way of remembering information in the long run. However, the length with which over-learning is beneficial is currently up for debate.

A study in 2005 by Doug Rohrer and colleagues suggests that over-learning doesn’t benefit in long-term retention scenarios with intervals of nine weeks or more. Regardless, additional testing as opposed to additional studying of previously recalled words did have a big positive effect on later recall of the material.

So, to study more effectively for your exams, the key take home messages are two fold:
1) Alternate between reading your study notes and doing practice tests if you want to better retain the information you’re studying.
2) Don’t quit studying information that you have already recalled successfully on a practice test if you want to retain the information in the long term.