As the prevalence of Autism Spectrum Disorder (ASD) increases, School Psychologists (SPs) and Educational Psychologists (EPs) have an increasing role in assessing children with ASD. The systematic literature review aimed to provide an overview of the tools and processes EPs and SPs are using to assess children with ASD or possible ASD. Studies published between 1996-2016 were identified from four databases. Eight studies met the inclusion criteria, and were analysed using quality and relevance frameworks. Six studies were included in the final review. Commonly used tools are identified and discussed. The SLR drew some tentative conclusions around the range of tools used by SPs in the US. The small and dated UK sample means that limited conclusions can be drawn about current EP practice. Due to the gap in current knowledge around how EPs assess children with ASD or possible ASD, a questionnaire was developed and distributed to EP professionals in the UK and Ireland in order to gain an up to date picture. Data from 161 participants were used in the analysis. Analysis of the quantitative data involved descriptive statistics and content analysis was used to analyse the qualitative responses. Frequently used tools and the factors that seem to influence decision making around the choice of assessment are discussed. Implications for EPs' assessment practices and directions for future research are discussed. Having considered evidence based practice and practice based evidence, the final paper discusses dissemination of evidence to professional practice. A strategy for disseminating the findings of the empirical study to the profession is outlined.