Countries seek to implement sustainable policies for supporting professionals working with students with an autism spectrum disorder. These policies can advance more slowly in developing states like Romania and Greece. As such, this study aimed to investigate the reported knowledge and training needs of professionals working with ASD students to inform policymakers. Using a cross-sectional design, 475 Romanian and 211 Greek specialists completed an online questionnaire on the following dimensions: diagnosis and assessment of ASD, management of behavioural problems in ASD students, communication skills, technology, teaching, and e-learning platforms. The results showed that Greek professionals have higher levels of ASD knowledge compared to Romanian respondents (MGreece = 15.2, SDGreece = 4.22; MRomania = 13.7, SDRomania = 3.88; U = 39703, p < 0.001). There is also a significant need for training on all the investigated dimensions in both countries, with greater training needs in Romania than in Greece (MGreece = 26, SDGreece = 2.98; MRomania = 27.2, SDRomania = 1.84; U = 35556, p < 0.001). Both countries reported the lowest level of knowledge in innovative teaching technologies and high training needs using an e-learning platform. The results emphasise important gaps in the educational programmes for ASD professionals.