This paper aims to understand how teachers' attitudes are contributing to or hindering the educational inclusion of students with autism spectrum disorder (ASD). Implicit and explicit measurement of the attitudes of fifty pre-service teachers towards ASD before and after a short-term training on Autism is presented. The explicit measure used was a Likert-type questionnaire, while the implicit measure was a Single Target Implicit Association Test (ST-IAT). After statistical analysis of the data, it was found that prospective teachers' explicit attitudes were positive before the short-term training, and they were significantly better after it. Conversely, participants' implicit attitudes were neutral before the short-term training, and no significant difference was found after it. Additionally, no statistically significant relation was obtained between explicit and implicit attitudes, either before or after training, which suggests that the used instruments measure different attitudinal constructs. According to the remaining findings, it is concluded that explicit attitudes may be more prone to social desirability bias than implicit ones, implying that future attitudes research regarding sensitive topics such as the educational inclusion of students with Autism should combine both measures. Moreover, implicit attitudes seem more difficult to change than explicit ones. Some implications for pre-service teacher education are discussed.