Therefore, "Scale A Teacher" would likely refer to a teacher at the lowest or entry-level of a particular school district or organization's salary scale. However, this is highly context-dependent. The specific meaning will vary greatly depending on the school system or country in question.
To understand what "Scale A Teacher" means, you need to know the context — which school district or organization uses this terminology. Check the relevant collective bargaining agreement, human resources documents, or contact the school system directly for clarification.