For the professional ethics issue, I would start with ERIC (General Education tab of the Graduate Education libguide: https://libguides.brenau.edu/grad-ed). I chose Advanced Search and put "professional ethics" in one box and teacher in another box. Make sure you use quotation marks around "professional ethics" to make it search that exact phrase. Next, I filtered by "peer-reviewed" on the left side. That gave me 123 results. Several of the results look pretty good, depending on how recent you need the article to be and what specific area of ethics/education you're looking for.
For the class size question, I would also start with an ERIC advanced search. Look for "class size" in one box and behavior in another, then filter by peer-reviewed. Run another search for the question about class size and academics. That's pretty broad, so think about what *kind* of academics you're looking for. Would terms like "student success" or "outcomes" or "graduation rates" measure what you mean by "academics"?
One last tip: the idea of class size is mentioned a lot in articles that are only vaguely about class size. In the "class size" search box, you can change the drop-down field to "TI title" to find only articles where class size is mentioned in the article title, or "SU Descriptor" to find articles where it's been "tagged" as being about class size. Finally, think about whether "student-teacher ratio" could be used as another descriptor for "class size" in your case.