The recent boom of so-called generative artificial intelligence (AI) applications, namely large language models such as ChatGPT, took the public discourse by storm, disrupting many fields and industries. Education, being one of them, was left with little to no information about the impacts of such an unprecedented technology, let alone holistic methodologies on how to reflect and adopt it. Therefore, many educators rush to adopt policies banning the technology but find themselves incapable of reliably detecting the cheaters. All in all, the distribution established chaos in the education community. To address this problem, we propose a methodology assessing relevant information for educational institutions that can guide their decision-making around generative AI practices and policies. We demonstrate this methodology in a Czech high school, conduct a student assessment study, and make the dataset available to the public.