Effective training is usually role-specific: designers need to understand color contrast and focus states, developers need semantic HTML and ARIA fundamentals, content writers need to know how to write good alt text and link text, and QA staff need basic keyboard and screen reader testing skills.
Organizations that invest in training alongside a one-time audit tend to see accessibility issues decline over time as they are introduced, while organizations that rely purely on periodic outside audits without building internal skill tend to see the same categories of issues recur release after release.