It's the time of year where students are poring over their books, trying to ensure they are prepared for their exams.

Revision charts, highlighter pens and sticky notes around the room are some of the methods people use to ensure information stays in their mind.

But now psychologists in the US warn many favourite revision techniques will not lead to exam success.

Universities, schools and colleges offer students a variety of ways to help them remember the content of their courses and get good grades.

These include re-reading notes, summarising them and highlighting the important points.

Others involve testing knowledge and using mnemonics - ways of helping recall facts and lists, or creating visual representations of the knowledge.

But teachers do not know enough about how memory works and therefore which techniques are most effective, according to Prof John Dunlovsky, of Kent State University.

Help - or hindrance?

He and his colleagues reviewed 1,000 scientific studies looking at 10 of the most popular revision strategies.

Image caption Highlighting may not help

They found that eight out of 10 did not work, or even hindered learning.

For example, many students love to take a highlighter to their notes.

But Prof Dunlovsky's research - published in Psychological Science in the Public Interest, a journal of the Association for Psychological Science - found that picking out individual phrases in florescent yellow, green or pink can hinder revision.

"When students are using a highlighter they often focus on one concept at a time and are less likely to integrate the information they're reading into a larger whole," he says.

"That could undermine their comprehension of that material."

But he's not suggesting that highlighters should be abandoned as he recognises they are "safety blankets" for many students.

Plan ahead

Teachers regularly suggest reading through notes and essays from lessons and making summaries.

But Prof Dunlovsky says: "To our surprise it turns out that writing summaries doesn't help at all.

HOW THE TECHNIQUES FARED Elaborative interrogation - being able to explain a point or fact - MODERATE

- being able to explain a point or fact - Self-explanation - how a problem was solved - MODERATE

- how a problem was solved - Summarising - writing summaries of texts - LOW

- writing summaries of texts - Highlighting/underlining - LOW

- Keyword mnemonics - choosing a word to associate with information - LOW

- choosing a word to associate with information - Imagery - forming mental pictures while reading or listening - LOW

forming mental pictures while reading or listening - Re-reading - LOW

- Practice testing - Self-testing to check knowledge - especially using flash cards - HIGH

- Self-testing to check knowledge - especially using flash cards - Distributed practice - spreading out study over time - HIGH

spreading out study over time - Interleaved practice - switching between different kinds of problems - MODERATE

"Students who go back and re-read learn as much as students who write a summary as they are reading."

Some revision guides advise using memory aids, or mnemonics.

Prof Dunlovsky says they can work well for remembering specifics, like Richard of York gave battle in vain, which allows people to remember the colours of the rainbow,

But he warns they are not applicable to other kinds of material. "They won't help you learn long passages or mathematics or physics."

So what does work?

Only two of the 10 techniques examined turned out to be really effective - testing yourself and spreading out your revision over time.

"Students who can test themselves or try to retrieve material from their memory are going to learn that material better in the long run", says Prof Dunlovsky.

"Start by reading the text book then make flash cards of the critical concepts and test yourself.

"A century of research has shown that repeated testing works."

This is because the student is more engaged and it is harder for the mind to wander.

He adds: "Testing itself when you get the correct answers appears to produce a more elaborative memory trace connected with your prior knowledge, so you're building on what you know".

Starting late

However the best strategy is to plan ahead and not do all your revision on one subject in a block before moving on to the next - a technique called "distributed practice".

Prof Dunlovsky says it is the "most powerful" of all the strategies.

Students who cram may pass the exam but they don't retain the material. Prof John Dunlovsky,, Kent State University

"In any other context, students use this technique. If you were doing a dance recital you wouldn't start practising an hour before, yet students like to cram for an exam."

Some students will always start late on their revision.

But Prof Dunlovsky says: "Students who cram may pass the exam but they don't retain the material.

"When they're going to be taking advanced classes in the subject, they are going to build on the knowledge they're developing, so I highly recommend distributed practice.

"A good dose of cramming that follows up on lots of distributive practice is the best way to go."

So do different techniques work for different individuals? Prof Dunlovsky says "no" - the top techniques work for everyone.

And experts think this paper could help teachers and lecturers help their students.

Dr Andrew Butler, of the department of psychology and neuroscience at Duke University in the US, says: "This paper is hugely important for the field and educational practice - it's about getting best practices into hands of educators."

But it is likely that students will still rely on what works for them, no matter what the science says.

Lea Corinth, who is studying international business and Spanish at the University of Westminster uses the re-reading technique - rated by the researchers as being of little use.

But she says: "I read over everything until I memorise it. It doesn't take too long.

"I make summary notes of everything important, put it in a folder and memorise everything."

But Abdul Harmetz, who is studying history at the same university, says: "I'm a crammer - I started revising yesterday and stayed up all night for my exam today, using old school techniques like copying everything out over and over again.

"The exam went all right actually."