What Works?
  • What is What Works?


  • Who is What Works for?


  • Why should I use What Works?


  • How do I use What Works?


  • How do I submit an intervention?


  • Get involved in What Works


  • Understanding the evidence base


  • The SEND Code of Practice


  • Glossary of terms


  • What Works Training Database


Understanding the evidence base

The evidence around interventions for children and service delivery can be complex. What Works aims to be clear and transparent about what constitutes good evidence and to provide the necessary information about interventions that will make the site a useful tool to support decision making. You may also be interested in our list of other useful sites about evidence-based practice.

Although randomised control trials and systematic reviews are usually considered the gold standard of research, to avoid excluding interventions which may achieve good outcomes but which have not yet been evaluated in this way, we have not limited the evidence base to these levels.

Instead, we have included a range of evidence levels representing a good level of evaluation. A set of criteria is applied to every intervention, ensuring robust and transparent decisions are made on which interventions to include and at which level of evidence.

For more information on the evidence levels and the criteria, please see our guide, which explains each of the criteria in detail, and two new support documents authoured by James Law and Jenna Charlton. The guide and support documents explain how the Moderating Group make their decisions about which interventions to include and what makes up a good evidence base, as well as providing links to further information on accessing and conducting research. 

Support Document 1 - Guidelines for Submission

Support Document 2 - Importance of the Strength of Evidence

We also aim to help practitioners stay up-to-date with other relevant research on children's speech, language and communication through our regular evidence updates


Strength of evidence versus strength of outcomes

It's essential whilst using the database to be aware of the important distinction between the strength of the evidence and the strength of the intervention's outcomes for children and young people. This is due to some interventions on the database not having wholly positive outcomes for children but still being included on the database because of the strength of research.  Strong evidence doesn't necessarily mean an intervention works well. Equally other interventions may only be classed as "indicative" in terms of research design, but the outcomes for children look very good indeed.

It is therefore important when making decisions around which interventions to use not to choose interventions based solely on levels of evidence, as an intervention at a lower level of evidence may be more appropriate and may show better outcomes.


Effect Sizes

Looking at the effect sizes of interventions on specific outcomes can support practitioners to interpret whether an intervention is appropriate for their setting. Effect sizes of interventions can  be viewed on theWhat Worksdatabase via a graphic which is linked to from each intervention’s page. Each graphic provides information on the outcome that the intervention had the largest effect on, the smallest effect on and the effect size for the primary outcome as stated by the researchers (in other words what the researchers were primarily looking at in their study).

Effect sizes were drawn from the study which provided sufficient evidence to calculate them given the means and standard deviations, these may not be representative of all the studies for this type of intervention.

For more information on this, see our animation and guidance here.

Why do interventions not make it on to What Works?

Interventions are not included if they have limited or weak evaluations; or evaluation information is not readily available in the public domain.



Inclusion on What Works does not constitute an endorsement from the Moderating Group or The Communication Trust either for individual interventions or the organisations that produced them.

Please click here to read a disclaimer from The Communication Trust, which includes some important things to be aware of when using What Works.